... the voice of a faithful disciple of science is entitled to be heard.My continuing researches on the discovery of climate change show that prior to Ignaz Venetz's 1821 prize-winning paper, the most commonly held views on the earth's climate were either that it had changed once, briefly, as a result of the noachain flood, or that the earth has been continually cooling since it was formed. It was also held by most geologists that all rocks which were not obviously of volcanic origin were formed in or by water.
It is very clear that Venetz considered that many rock types have been formed by glaciers, that there have been multiple glacial extensions - now called ice ages - and that these had been caused by changes in climate. He was of the view that some rock features could be attributed to lake outbursts, but rejected the general view of global scale floods.
I present here my translation of his posthumously published Memoire sur l'extension des anciens glaciers renfermant quelques explications sur leurs effets remarquables.
As before, I have retained older place names. Please note also that since Ventz's times the designations of various geological periods have been changed. It is for that reason that I have not attempted to translate every instance of an era, period or epoch with a specific term. Regardless of any consistency of terminology that I might inject, the terms would still be obsolete.
Comments are welcome. No translation is perfect and there is always room for disagreement about nuances. Please feel free to point out mistakes and to contribute suggestions for improved translation. This is science 2.0 - I am happy for it to be also translation 2.0.
The translation follows below this page break >>>
Memoir on the extension of ancient glaciers
containing some explanations of their remarkable effects
M. Venetz senior, engineer
Posthumous work written in 1857 and 1858
Translated by Patrick Lockerby 2011
This memoir from the hand of Mr. Venetz Snr., engineer, is a posthumous work, and seems neither finished nor complete in these existing parts. Despite these defects, the Editorial Committee believes that it acts according to the general intentions of the society by admitting it for publication. The committee has mainly been guided by two reasons: first, by a feeling of piety towards the founder of the beautiful theory of erratic transportation, which, like few others, has acquired rights of citizenship in geology and served as a starting point for a host of other important research, and secondly, because it is always interesting, even at a more advanced stage in science, to know the ideas of a man who spent his life among the great events he describes and who has created a subject for constant research and meditation. Indeed, just as, at the start of his career, Mr. Venetz became known to the scientific world by his work on older moraines, so also at the end of a long life devoted to a practical activity, he returned to his favorite subject and summarized in the present work the collection of all of his observations. Certainly, the voice of a faithful disciple of science is entitled to be heard.
The Editorial Committee.
The first part of this memoir was intended to be read at the meeting of the Natural History Society, held in Bern in 1858.
The author's intention was to give this work a much greater extension, to enter even into explanations of the causes of these phenomenae, if death had not unfortunately intervened in April 1859.
It is also regrettable that Mr. Venetz did not have more time available to deal with this interesting topic, but due to circumstances beyond his control, the injustices committed against him by a rich government of our Switzerland forced him to work hard which left him little time to devote to science, as will be seen later in his Biographical Notice.
At its meeting held in Bern in 1816, the Swiss Society of Natural Sciences was concerned for the first time with the study of glaciers.
It is to a memoir composed on this subject, and read by the late Mr. Charpentier before this society that I owe my admission as a member.
In this paper I had shown how the bodies which fell into the crevasses of glaciers reappeared on the surface in a greater or lesser time downstream of the fall.
The explanation of this phenomenon was contrary to the hitherto accepted hypothesis that the melting of glaciers was taking place mainly at the base, for it has been shown, on the contrary, it is almost exclusively on their surface.
In this paper I also explained that the main movement of glaciers came from the increased volume of water infiltrated and frozen in the many cracks and crevices that run through in all directions.
A second memoir, that I had produced treating of glaciers, was read during another meeting held in Bern in 1822.
I cited many facts tending to prove that in an epoch prior to our own the climate of the Alps was very much warmer than now, but was preceded by another which, in contrast, was much cooler than today.
This assertion was supported by the evidence of ancient moraines located in regions distant from each other and at considerable distances from the lower end of existing glaciers.
The meeting deigned to award a prize to this memoire .
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Encouraged by such success, I eagerly redoubled my observations and I conducted further research to find the limits of the extreme extension of ancient glaciers.
But without noticing at first, I was led step by step to the persuasion that the transport of erratic boulders, which one finds on the Jura, is due to the immense extension of glaciers and it is they which have brought them over such great distances onto the plains, over mountains and through the depths which have converted themselves into lakes.
I communicated my views to Mr. de Charpentier, who, at first, strongly rejected this theory.
"The earth has cooled down," he said, "instead of acquiring heat, there could not therefore have been such extensive glaciers."
Although the learned geologist would not accede to my opinion, I was not discouraged. I took him for a walk on the accumulations of erratic terrain and began the discussion by asking the cause of the formation of these accumulations of erratic terrain, and when I had explained the constitution of different stratified layers evidently deposited in water, but containing erratic boulders, he approved of my point of view.
This deposit, veritable glacial diluvium, is located on the east of the hamlet of Posses, near the salt mines of Bex, between two valleys. It presents a vertical wall to the west side.
On July 22nd, 1829, at the session of the Swiss Society in Grand St. Bernard, I
explained that the glaciers had once seen vast extensions and that it was they which have scattered, over various parts of the Alps of the Jura and of Northern Europe,
enormous blocks, in forming moraines.
In 1834, Mr. Charpentier announced at the society meeting in Lucerne that I was working on a dissertation on the extension of glaciers, while giving some details about this subject.
Mr. Agassiz, who was elected president of the Society for 1835, stayed for 6 weeks at Salaz near Devens where Mr. Charpentier resides.
The latter introduced him to the different regional terrains of interest to this new theory.
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My duties did not allow me to continue my memoir, Mr. Carpenter volunteered to do it.
His essay on glaciers was published in 1841, shortly after the studies carried out for the same purpose by Mr. Agassiz and published in 1840.
One can not ignore the impact and controversies that these works have caused. One knows also that the glacial theory is nowadays generally accepted.
Distinguished geologists, who shared the same opinion, have discovered at the foot of the Alps, as well as in Scandinavia and parts of the New World, facts which in their view, were not a production of old glaciers, while I am led to believe, based on their description, that with a more detailed study of localities and different phases of the extension of the glaciers, it will perhaps be possible to find the specific cause of the formation of these bodies.
Without pretending to give a sufficient explanation of these phenomenae, especially since the lands, where they act , are entirely unknown to me - I urge geologists to examine these facts from the point of view of which I shall speak below, and see if their existence can be explained in this way without recourse to an agent other than the glaciers.
There are some geologists who do not admit that the erratic terrains have been transported by glaciers, but attribute this transport to violent muddy currents.
This view was strongly refuted by Mr. Charpentier, yet I cannot refrain from saying a few words more.
First, without admitting the glacial theory, it would be difficult to explain the formation of masses of clay and silt spread in large quantities on the sides of mountains, sometimes on quite steep slopes.
These deposits are usually fine at the base, without any admixture of stone, are often covered with sand, upon which lies gravel mixed with stones and boulders.
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How also does one explain the deposit of clay mixed with gravel which, according to Saussure, constitutes at Travers, near Geneva, the bottom of the lake, also the bed of clay mixed with rounded boulders and erratic blocks which, towards the bridge over the Rhone near Moerel, forms the bed of this river.
If the defenders of currents of water can explain these phenomenae satisfactorily, and demonstrate how the erratic stone near the powder magazine of Sion came to be in the extraordinary position in which it is found - then we could begin to dicuss their theory.
Here is the description given by Mr. Charpentier in his essay (page 146 and 147) of that stone, the design is plate 6 and 7 of that essay.
"It (the big block) has an irregularly rounded form, although the surface shows no obvious signs of friction, its diameter is some ten feet. It is almost on the edge of a very steep slope and is supported only by three points. One of the supports is a wedge protruding from the bedrock which is a strongly quartzose talc schist."
"The second is a block of talc schist split from top to bottom and evidently detached from the bedrock. Lastly, the third support is a quartz sandstone characterized by a few grains of rose quartz and which I do not find nearby but up to five leagues upstream of Sion on the left bank of the Rhone, opposite the town of Leuk."
"The limestone block is likewise split through all its height, the gap between the two halves is but a few inches. The situation of this block on the edge of a kind of precipice, the way it is held in place and the vertical breaks, either of the big block itself, or of one of the supports, all these circumstances together can prove beyond a doubt that it was not placed there by a current, or broken by a horizontal shock; but it fell onto the place where it is found and that its fall cleaved it, breaking one of the blocks that support it."
I will try to explain the mechanism which has placed the block in this position.
Glaciers, meeting in their progressive movement mounds of solid rock, rise slightly against the barrier, causing crevasses on them.
Fiesch glacier gives us a striking example towards its lower end where a rock projecting in the middle of the valley, divides it in two.
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It is therefore natural that in the time when the ancient glacier still occupied the plain of Sion and greatly exceeded in height the mound of the powder magazine, the quartz sandstone rock fell into a crevasse in the glacier first and the limestone block followed it.
The violence of the shock from the fall, detached a fragment of rock shearing it in two, and split the block itself in the middle.
The whole has slipped a little, but the walls of the crevasse in the glacier growing narrower downstream arrested their movement of repulsion which, but for this circumstance, would have dropped the two halves of the limestone block separately from this unique position.
The glacier theory also explains the glacial deposits referred to in Articles 8 and 9. The last are moraines of which I shall make mention later. Those preceding are veritable glacial drift * ).
MM. Charles Martin and B. Gastoldi in their essay on the superficial terrains of the Po Valley, in the Turin region, compared to those of the Swiss plain - divide these terrains into glacial formations and aqueous formations **).
Within the glacial formations they include the ancient glacial moraines and scattered glacial terrains ; within aqueous formations, the fossil-free alpine drift, pliocene alluviums, and the marine beds which support them.
They attribute the aqueous formation to a geological era more ancient than the period of ancient glaciers, saying that the alpine drift predates the glacial period, perhaps has no connection with it.
M. E. Desor in his memoir on the erratic phenomenae of Switzerland compared to those of northern Europe and America ***), distinguishes the erratic phenomenon of Scandinavia from that of the Alps in that it embraces a considerable period,
*) Essai sur les glaciers, p. 63 et seq.
**) Bulletin de la Société géologique de France, 2nd series, volume VII p. 554, session of 20th May 1850.
***) Actes de la Société helvétique des sciences naturelles 1852, p. 97.
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during which, he believes, one can distinguish several very marked major phases or epochs, namely:
1. The epoch of the polishing of the rocks, during which Scandinavia was probably flooded as at present;
2. The epoch of Osars, during which Scandinavia is found to have been covered by the waters of the sea to a considerable height;
[ there is no item 3 in the incomplete original.]
4. The epoch of the transport of superficial blocks, which ends the period of Osars and after that in which Scandinavia was again submerged and assumed its current contours.
"In Switzerland, on the contrary, he says, we are accustomed to consider the erratic phenomenae as the work of a single agent (either a current or a vast glacier) that would, all in one go, polish the rocks, heap up the piles of boulders and transport the blocks to their current positions."
I am of the opinion that these different products were from the same cause as the alpine drift, as well as the ancient glaciers that have polished rocks, formed moraines, including Osars, and transported the boulders, are products of this cause; but that they were not formed all at once and that on the contrary, their formation was separated by intervals very long in years.
Indeed, if one finds a smooth rock on which is a moraine of pebbles or boulders, one can prove that the rock was reached twice by a glacier: the first, when the rock was subjected to polishing and the second, when the moraine was deposited.
Glaciers can smooth, scrape, rub and scratch the rocks without having a considerable thickness.
These results can not arise except under a great weight in motion.
While the glaciers are in-progress, they sweep up everything movable that they encounter along their way.
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We can except nothing but the gravel deposited by the streams which flow out, on those glaciers whose lower end slides occasionally in advancing, and deep moraines, on which their movement has ceased from some cause.
These frozen masses cannot therefore deposit materials on the rock that they wear away, but they push it further and form the terminal moraine before retreating.
But this moraine is not formed other than very slowly.
Indeed, when after a series of cold and wet years the temperature rises to the point where the glaciers begin to diminish in volume, this reduction occurs first on the high and low snow fields while the glaciers, properly speaking, continue to increase in length.
By the reduction in snow fields, the glaciers are found more and more in process of becoming more compact and less mobile.
Once the top of these ice masses has declined to the point that their weight and freezing of infiltrated water can no longer replace the ablation at the lower end, the glaciers recede.
But at the end of a glacial expansion, the temperature does not rise in a uniform and permanent manner.
Rather, it occurs in years when the mean of the temperature becomes variable.
Several warm years are sometimes succeeded by others which cause the glaciers to advance anew. During this variability in average temperature, glaciers by their continual movement, replacing the ablation to a greater or lesser degree, almost wholly discharge the debris they carry, and do it beyond the rock they polish , as we have already said.
Onto this rock can fall only the sparse scattered debris that glaciers leave as they retreat.
Moraines, covering polished and grooved roches moutonnées, are not the only clues that demonstrate to us more than one glacial extension. The quantity, spacing
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and positions of the erratic deposits provide us with others no less conclusive; especially for the reason that rocks covered with snow or ice do not allow of
other alterations than those coming from the movement of ice masses, accompanied by small quantities of silt and sand.
This requires that the mountain slopes and walls of the rocks were again uncovered, after their envelopment in the ice and their exposure after a long term of years to the weather of the seasons in order to furnish on their upper surfaces the materials that form the moraines, which were clearly arranged in a period later than that which had already caused a larger extension of glaciers.
Some years before the publication of the essay on glaciers, I wrote a letter to Mr. de Charpentier with a map of Valais, on which I had noted that three different extensions, according to my observations, the glaciers of the Valais must have had before, not including those which had produced moraines located close to current glaciers, such as at the foot of that of the Rhone.
I showed him, in this letter, that each one of these extensions was probably separated from the others by a very considerable period of time, during which the glaciers, reaching their maximum extensions, then retreated and advanced anew until they had arrived at another end of their progress, but that this end had arrived before they could reach the extent and volume that they had acquired in the preceding extension.
Subsequent observations caused me to assume that these alternations were even more numerous and that the greatest development of the glaciers had spread over an area much larger than that which is assumed today.
These indications reach over but a very limited part of the Alps, I will give some details about the disproportionate extensions, that the Rhone Glacier has had, at least, in four different epochs separated as I stated by great lapses of time, during which the climate had reached the point of reduction of the glaciers to a smaller area.
These four extensions are:
1. The one where the glacier had passed the summit of the Jura. It is the largest and oldest development which, to my knowledge, can have been recorded by the erratic deposits.
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2. The one where the Rhone glacier, with some tributaries, had again occupied the basins of Lake Geneva and Lake Neuchâtel, and all of southern Switzerland.
3. The one where it reached as far as Noville.
4. Finally, the last, which must be attributed to a prehistoric time, is that where the Rhone glacier deposited its terminal moraine at 6400 meters from its current foot, moraine on which lies the village of Obergestelen.
We come now to the facts from which we can assume these various extensions of the glaciers.
In his essay on glaciers, Charpentier gave (page 159 et seq.) the description of the erratic terrain forming a fringe on the southern slopes of the Jura and, on page 269, he takes the deposit to be a moraine formed at the time of greatest development of diluvian glaciers.
The highest point of that deposit is on the Chasseron at 1007 meters (3100 feet) above sea level, which is 603 meters below the summit of this mountain.
However one finds polished and grooved roches moutonnées on the Jura, above that erratic terrain.
This fact is visible on several points, especially on the south-east of Mount Tendre on an estate overlooking the forest located above the village of Mollins.
De Saussure already mentioned, in art. 353 of voyages dans les Alpes, the coming together of stones from these areas in the immense heap of stones that you see below Jougne.
MM. Martin and Gastoldi say: *) "Many Swiss geologists, MM. Studcr, Thurman, de Charpentier, Blanchet and Guyet, have noticed outside the line of boulders on the eastern slope of the Jura, fragments and isolated blocks of Alpine rock of pebbles, quartz, euphotide, protogine, angular and striped alpine limestone, which can be followed to the outskirts of Lyon, since
*) Bulletin de la Société géologique de France, 2nd series, vol. VIII, page 598.
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on the heights of the Croix-Rousse, Mr. Fournet found alpine blocks of 6 cubic meters and striped stones identical to those that make up the moraines of the glaciers today. "
Charpentier himself, continuing the description of the moraine of the Jura, said on page 161:
"From Butet it went towards St. Croix, but did not reach this village, and without rising to the Col de Nevreaux which separates the St. Croix valley from the Val de Travers."
"The pebbles of alpine rock found between this village and the pass, belong to drift."
But these pebbles are in a clay bed, in which they dug the cellars of the toll house situated above the village of the col.
The detritus of limestone rocks cannot constitute true clay. This deposit could not therefore have formed on that limestone mountain except by water released from a glacier in the Alps and collected in pools in this locality during the retreat of the glacier.
These facts suffice to prove that there once existed a diluvian glacier, rising significantly above the level of the highest parts of the moraine of the Jura, described by Charpentier which has carried alpine rocks beyond the top of this mountain chain.
But the erratic terrain, coming from the Alps and belonging to this extension, are still only rarely recorded in the geological literature. We know of only a few instances.
However the largest expansion of diluvian glaciers must have spread the erratic terrain the most.
A vast field of research is still open in this regard ; I shall discuss the study of this subject later.
I would further remark that there is still a large deposit of this terrain at the foot of the south-east slope of the Jura.
This terrain comes largely from the limestone and primitive rocks of the Alps and the same from the Jura.
Their existence is easily explained on reflecting that in the period when snowfalls
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were so frequent and abundant in the Alps, the glaciers, as a result of their accumulation, advanced to the top of Jura; on this mountain also enough snow dropped to form glaciers.
The latter, descending into the plain before the arrival of those from the Alps, bringing also their debris like that of the Alps; but at the point where they met, their deep frontal moraines must have remained largely in place, despite their continued progress which, therefore, could have no effect except on the sides and in increasing the thickness. *)
This basin should be filled because of the continual push of Alpine glaciers which, descended from regions much higher than the Jura, caused the progress of those coming from the said mountain to stop completely on this side.
It is even likely that at the time of greatest expansion, the glaciers and snowfields took on an almost uniform slope from their surface, the highest of the Alps up to the summit of the Jura, their pinnacles were enveloped in ice or snow fields.
But as soon as the volume of the first glacial extension decreased, the decrease took place at a lesser rate in the heights than in the lower regions.
Despite this difference, the true glaciers advanced again while the snow fields declined beforehand, as has been said above.
As long as the snowfields of the Alps were increasing the volume of the glacier and as long as the volume of the Rhone, with its tributaries, was filling the great Swiss basin to the top of the Jura, the glaciers of this chain of mountains could not but develop on the French side and, the Rhone Glacier could not but penetrate into the interior of the chain and carry the stones over the cols of Nevreau, Jougne, St. Cergues, Dapples, and enter through the gorge into the course of the Rhone as far as Lyon.
*) When a glacier meets an immovable obstacle, the progressive movement ceases at the base. - These are the upper and middle layers of the glacier, excited by the weight of the upper part, which increase in thickness and mount up against the obstacle.
Distel glacier in Saas Valley provides us with an example.
This glacier, descending, crosses the valley and rests against the opposite hill, forming a lake upslope of the crossing.
The annual layers that this glacier acquired in the upper regions are distinguished from the more sandy lower parts.
From this fact it is recognized that the movement of this glacier is that which I have indicated in this passage.
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But it seems that the increase ceased before the alpine blocks were able to pass significantly beyond the cols of the Jura.
As soon as the retreat of the glacial extension embraced its full extent, the movement of this mass experienced great changes.
Water from rain and melting ice, unable to remain in the interior of glaciers, formed huge streams of water which are known still at the bed in several places.
The erratic terrain of the Jura, so well described by Charpentier, appears to me to be partly the result of this first extension, but it does not indicate at all the height which it reached.
On the contrary, the erratic deposits clearly show that they were formed during the reduction of glaciers, or at their retreat.
Indeed, starting from the highest elevation above Bullet and Mont Turket *) the moraine descends from the east side in order to approach Bonvillars, Corcelles and Concise at 443 meters above sea level; it then rises in the Travers valley towards Couvet and Moutiers, at the height of 740 meters, to descend and then rise again on the Cheumont slopes. Finally, it ends in the plain below Soleure.
From the west side, on leaving Bullet, it follows a line of uneven height to reach also to the plain of Gex less than 609 meters in elevation.
Although the surface of seas of ice frequently presents undulations which, at a distance, resemble large waves, one can not reasonably assume that when it was located 780 meters above Lake Neuchatel, the Rhone Glacier could present such a height variation, especially as the glacier was fed by those which descended from the high mountains of Berne and of Savoy.
The cause of the piling of the moraine at heights so different comes, in my opinion, from a more or less considerable elevation of the cols of the summit of Jura, from their shape and from the vales or valleys that separate these summits.
On that depends the volume and shape of the ancient glaciers which unite the Jura with those of the Alps.
*) Essay, page 159.
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On that depends also the movement of glaciers during their decline and the form of the erratic terrains they left behind.
After the peak elevation of 1087 meters, they terminated on reaching a ridge with steep slopes, like the Cheumont, the Chasseron, Mont Suchet, Mont Tendre and the Dole, the glaciers which commenced behind or at the side, quickly descended on the lower plateaus.
Since this plateau is elevated like that found above Bullet and is still dominated by the Chasseral which is almost a sharp edge, the glacier can not advance more before meeting the glacier of the Alps, than those which descend the valleys of St. Croix and the valley located between the Suchet and the Aiguilles de Beaulmes.
It could not therefor occupy an area as large as these last, which, probably, came close to Chatillon and formed the moraine which forms the basin of Beaulmes.
Thus also with the plateaus of Bierre, of Gex and others where the glaciers, descending valleys surrounded by the highest summits of the Jura, occupy an even greater extent before meeting that of the Rhone and the Arve.
During the growth of glaciers in the Alps, these summits offered obstacles holding back those of the Jura and obstructed their passage over the cols of the mountain; but when they decreased, the summits pierced the first of these ice masses that covered all the land.
It is thus on the plateaus of the southern side of these elevations that the moraines could have been deposited at the greatest height, but it was necessary that they had been protected from glaciers and falls of avalanches in the 2nd glacial period in order to have remained in the position where they were during the first.
I would also note that considerable deposits could remain in the side valleys, such as those to the west of the Dent de Lys, because the glacier, filling the plain, had blocked their exit before they were filled by the glacier that had formed on top of these valleys.
Erratic deposits could equally remain behind the high isolated hills, as to the north of Chalet a Gobet, at the height of 860 meters, one finds a moraine currently serving as a gravel quarry.
In such localities, the movement of the glacier could not remove them during its growth, but could well increase them during its decline.
The extension of the glaciers, which followed the one of which we have spoken, has left many accumulations of erratic terrain in Valais, which must be attributed to the oscillations which it experienced during retreat, the maximum of glacier height in Valais had already passed at that period all the points not reached by glaciers in the third extension.
This is not the same in the canton of Vaud where the erratic terrain of that epoch can be made out in many places.
On the ridge overlooking the village of Gryon, the moraine of this extension is 1230 meters above sea level
Above the villages of Huémoz and Corbeyrier, it delimits beautiful valleys in which one recognizes small glaciers which, descending from the surrounding summits, have met the great glacier.
We find the moraine near Puidoux, below Savigny, west of Clef-au-Moine and the church of Croisettes.
During its maximum height, the glacier had a nearly 4% slope from the exit of the gorge between the dents du Midi and dents du Morcles up to the face of the Croisettes, where the moraine is found at the height of 729 meters above of sea level
The Rhone glacier then spread into the valley of the Venoge until it was met by the glacier descending from the summits of the cantons of Fribourg and Bern.
We find the remains of its height to the west of La Sarraz on a high projection of rock which overlooks the right side of Venoge.
On the top of the Riere Rance hill, many erratick boulders are also found near a building.
The moraine passes north of the village of Valeyres, below Mount Cherand; it is north of Agiez of Boflens and of Croy.
The waters of Nozon and Venoge, probably forming a lake between the glacier and the Jura, caused changes in the erratic deposit, but the moraine appears to be quite distinct.
From the projection of rock of which we have spoken, the moraine continues without interruption against Dizy and passes north of Cossonex, near St. Livres.
It is topped by hills that seem to come from deposits in the crevices of the northern glaciers.
The moraine of Lausanne, on which is built the Rue du Bourg and which extends to Ecublens, must by its volume be attributed to the time of this second extension.
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We shall discuss below, § 30, the reason why this moraine is found some 200 meters below the height that the glacier had reached at that time.
The many sources that give rise to the river Aubonne, often interrupted the terminal moraine.
So will it be that towards the end of the stationary period or the beginning of the retreat of the glacier, it will have formed the glacial alluvium of which we see accumulations descending from Colombier against Yens and Lavigny *) to meet beyond the river on Aubonne, at the Signal de Bougy, and from there on the hill to the west of the village of Chatel at 763 meters above sea level.
To the west of the hill of Chatel, I recognized in 1841 in travelling along the new road, leading to Molard at Burtigny, several places where the boulders are not stratified, that is to say, they are moraines.
Between the rivers Promenthoux and Versoix, deposits are unknown to me, but from the course of the latter river one may already presume that it was diverted from its natural course by the moraine of the second extension.
Having made a trip from Geneva to Gex, I saw at Ferney that the chateau of Voltaire is located on the moraine, as also the villages of Grand and Petit Sacconnex.
De Saussure indicating, § 51 and 54, the nature of the soil on the hill on which the city of Geneva is built in part, and also that of St. Jean, did not suspect that their formation was due to ancient glaciers.
But his description of this soil, proves to me that it is the result of two major glacial extensions.
This is what he says in § 55 of 'voyages dans les Alpes':
"The village (Cartigny) is situated on a very extensive plateau, elevated 178 feet (58 meters) above the level of the lake. The Rhone which passes at the foot of this plateau, is 77 feet down from Geneva below Cartigny, and therefore the river runs 255 feet (between 82 and 83 meters) lower than the plain on which the village is located.
The whole of this height of 255 feet (between 82 and 83 meters) is cut at the peak above
*) The construction of the new Aubonne road uncovered the many strata of sand, of gravel, and of stones that compose this terrain which formed at the same time as water melted the edge of the ice holding it against the mountain.
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Rhône in a place called the rocks of Cartigny.
The terrain undermined by water that runs between the layers, suffered considerable landslides, but the parts best tied together have remained and form here and there types of irregular towers and pyramids of very great height.
These pyramids that threaten ruin, viewed from the edge of the precipice, form a wild and terrible aspect, which contrasts sharply with the beautiful landscape that we see the other side of the Rhone.
If one goes down to the bed of the Rhone alongside its cliffs, we see that the terrain is composed at first of topsoil, then of horizontal beds of sand and gravel, and then thicker beds of a very fine sand.
All these beds together form a thickness of about 60 feet (19. 49 meters) and are followed by an almost uniform layer of clay, about 70 feet thick (22. 71 meters) and mixtures here and there of scattered stones.
In this clay, there are beds of sand, gravel and pebbles that form between them the 125 feet (40 meters) remaining down to the river bed.
The top half of this space presents loose and rolling stones, but the bottom half offers some which are (linked) by a limestone cement which forms a kind of pudding.
One sometimes finds in the interstices of these stones calcareous spar crystallized in a confused manner in rectangular laminates."
The beds of sand, gravel and pebbles, which are some 125 feet above the Rhone, seem to me to be the result of the first glacial expansion.
At that time, the glacier of the Arve and those of the French Jura met in the plain of Geneva and left their deep moraine (see Vogt).
Once the glaciers of the Rhone had joined, the entire ice mass must have increased in thickness until, surpassing the top of Vouache, it was able to extend from the west side and form a deposit of primitive rocks.
But during the retreat of glaciers, the melting of the ice, taking place to such a large extent, must have raised the river Rhone in the gorge separating the Jura from Vouache to such a height that in the lower plains to the west of Geneva, it formed a lake in which the waters of the Arve could create stratified beds.
In the second ice age, the glaciers of Jura returned, the first in the lower plain.
That of the Valserine closed the passage of the Rhone and formed a lake which exceeded the current height of Lake Leman by about 200 meters.
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The murky waters of the Arve pouring into the lake, produced a clay deposit and when the glacier reached there, it lost the pebbles which, as it floated and melted in the lake it let fall here and there in clay.
That is how on the second arrival of the glacier of the Arve the 70 feet layer must have been formed, and the clay soil which, at Travers, constitutes the lake bottom.
But in arriving there, it covered the soil of the deep moraine and shaped the stratified sedimentary terrains which cover the clay bed of the canton of Geneva.
In the third extension of the diluvian glaciers that of Rhone almost reached the current basin of Lake Leman.
The hills between Chessel and Noville are, in my opinion, the moraines of that glacier.
But MM. Morlot and Troyon, attribute them to the rockslide of Mount Taurus. *)
At first glance, this assumption seems likely, because of the height of the mountain that dominates this country, but the debris of fallen rocks usually stops at the foot of the rock from which it was detached.
They form a half-cone whose base is surrounded by the larger blocks of the landslide.
But the present course of the Rhone is a small plain separating these hills at the foot of the mountain.
There is also in this area a half-cone of fallen stones, at the foot of which lies the village of Evouettes, but it is at the end of a valley and crossed by the Tovets stream.
The distance between the foot of this accumulation of rocks and the hills between Chessel and Noville is at least 12 meters.
I have not had occasion to examine this issue more attentively, but many of these mounds seem to me to be obviously moraines.
If one objects that they contain no stone belonging to the high mountains of the Valais, I shall quote Vouvry in support of what I say; the church
*) It might thus be assumed that at the time of the rockfall of mount Taurus the mouth of the Rhone was found in this country at the foot of the mountain, that it fell so rapidly into this river at the edge of the lake that a part has splashed back, with the debris of the mountain, with sand and with gravel to the distance where one finds these hills.
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of this place is located at 1600 meters and built on a half-cone of stones and gravel containing huge blocks of granite.
In the canton of Vaud one can easily follow the trace of the deposit that the glacier has formed from the Cemetery of Chessel to Roche.
The village of Vervey is built on an accumulation of rock debris and limestone blocks that appear to have been part of a glacial band, interrupted by a crevice into which these materials have fallen.
The lateral moraine of this glacier is found in Yvorne and near the Aigle, south of the Doret house, it supports a great rounded boulder which seems about to fall onto the highway.
This moraine climbs up against the steep rocks overlooking the Ormonts road at the entrance to this valley.
Beyond the high hill of rock which, to the east of the Aigle, advances towards the plain, the erratic terrain reappears above the hamlet towards Chiez.
But here, it contains large blocks from the mountains of Valais.
We see them in a vineyard above the highway.
This circumstance shows that the Ormonts glacier was joined at that time to that of the Rhone and that the erratic soil, which is found on the right of the great valley between Aigle and Noville, is a production of the ice coming out of that valley.
Between the said vinyard and the village of Oron, the moraine is very remarkable in that it is carried away in part and that its consistency is of sand, gravel and pebbles of gypsum containing rare pebbles of primitive rocks.
Granite blocks are found on the hilltops of St. Triphon and Charpigny *) and of Montet, while the lateral moraine reappears to the east of Ollon, passing below Antaigne and the hamlet of Fenalet.
*) We see from the highway the small moraine that is located in the middle of the northern end of Charpigny hill, behind which the waters, coming down the valley below Panez, have caused an elevation of the land by destroying the Moraine .
What is remarkable, is that to the east of this end of the hill the soil shows graduations, meeting in an arc behind the hill; this indicates that the soil was pressed back by the bulging that the glacier experienced for several winters before disappearing.
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On the Valais side, the remains of this extension are found not only in Vouvry, but also on the side of the limestone mountain below the rock protusion overlooking the village of Collombey just above Monthey where a large branch of erratic blocks, described in the essay on page 139, crosses the mountain.
These are the blocks of granite, especially the stones of Murguets which during the walks and discussions already been mentioned above, I used as an argument to prove to Charpentier that this band was formed by a glacier. *)
You can follow the traces of that extension of the Outreviege glacier, above the village of Verossar in Mex and opposite, towards Alesse.
In Ravoire, this glacier has formed a moraine containing huge blocks of granite that traverse the whole mountain below the summit of steep rocks overlooking the islands of Otan to the Col de la Forclaz.
To that period also belongs the granite moraine which contains Lake Champex on the south, located above Orsières, and the huge deposit of blocks of granite at Plan-y-Boeuf, separating the valley of Ferre from that of Entremont.
I could indicate many places in Valais where the terminal and lateral moraines marked the extent of the glaciers of that period, but I will cite the Burgspitz mound, above Brigue, which is surmounted by a chapel, and another mount located to the west of the former.
These mounds consist of erratic deposits, as well as the terrain furrowed vertically by small valleys that extend from there to the precipice overlooking the Saltine above the village of Lingwurm.
In this terrain, snaking through the Simplon road, one finds blocks from the Jungfrau, proof that at that time the Aletsch glacier filled the valley of the Rhone to this height.
The glaciers of the fourth and last epoch, which preceded historical times, formed many moraines by which one can judge their extent; all the side valleys of Valais furnish ample examples.
I shall mention here some of the most remarkable.
The Rhone glacier was then extended, as we said above, to Obergestelen; the church is built on the same terminal moraine.
This glacier has left
*) Also he engraved my name on the stone which served as a support to the one that carries his.
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on both sides of the valley distinct remains of the lateral moraine; these moraines show us that the glacier had a steep slope.
The church and the village of Biel are also built on the terminal moraine that came out of Vallithal.
The Fiesch glacier formed a superb moraine on both flanks, like a greatly sloping road.
The Aletsch glacier extended to Brig. The right abutment of the Naters bridge is based on the moraine which leans in a semi-cone against the rock protruding from the foot of the mountain, over which passes the road to Naters at Mund.
This moraine is found at the top of this road, where it forms three distinct ridges. Riere, Weingarten, the triple moraine to the left of the glacier, is quite recognizable, but the ridges are farther apart than on the rock to the right of the glacier.
It was during this extension that the Aletsch glacier blocked the course of the Rhone opposite the outlet of the Massa, forming a lake in which the murky waters of the Rhone have left a deposit of clay mixed with pebbles and stones fallen from the glacier.
That, in my opinion, is the origin of this clay-gravel layer mentioned before, § 9, which came under the Rhone river to the mill of Morell.
At that time, the glaciers of the main valley of Saas descended to Almagel, and those of the Fee joined them and passed them a little further on.
The Vogelegge (Bird Hill) is the moraine they formed between them.
The foot of the mountain on the right of the Viege contains many blocks of gabbro carried by the Allalin glacier, while a little further downstream, before reaching the parochial village of Grund, these stones are replaced by serpentine from the mountains of Fee.
The erratic terrain, on which is found the Chapel and the hamlet of Trient, is the terminal moraine of the glacier of that name which was deposited at that time.
It is unnecessary to go into further details of facts so numerous demarcating the limits of this extension of glaciers; however, the moraines formed by the Salen glacier are worth mentioning.
This glacier, which now ends at the entrance of a lateral valley, crossed the valley of Ferrot almost at a right angle and leaned heavily against the opposite hill;
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on the left is seen the moraine at over 100 meters above the bottom of this lateral valley.
It extends along the main valley until near the village of Praz-de-Fort, where it is divided in three.
On the right, the moraine forms a wooded hill over 30 meters high.
In the middle an immense block is found at the summit.
The Dranse, arrested in its course, must have formed a lake upstream of the glacier which, in bursting its barrier, has probably occasioned the devastation that has left along the river such a large quantity of round granite blocks from Praz de Fort to Sembrancher, especially at the mouth of the Ferret valley.
The moraines shown so far to support the assertion of the four different extensions of the glaciers, referred to in § 24, mark out only approximately the height which the glaciers of each epoch reached, but there are others which, although located, like that of Lausanne at Ecublens, noticeably below this demarcation, should, because of their size, be attributed to one of those glacial epochs.
These are the results of the movement that glaciers have experienced during the almost stationary state, or during their decrease.
Indeed, in places where, during the maximum of their extension, the edge leaned against a part of the mountain suitable for receiving a moraine, it was deposited at the height which the glacier had reached.
But in places where two glaciers, arriving from different areas, have met, the moraine could not be formed except at the point where, because of their diminution, they separated.
That's why the moraine of the Jura described in the essay by Charpentier, page 159 and following, occupies places so unequal in height.
In places where, between the ground and the glacier, pools of almost stagnant water were formed, the moraines were converted into glacial alluvium. *)
*) Essay, page. 63.
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When these almost stagnant waters were fed by small streams, these alluviums formed alluvial cones where the silts, occupying the base, are covered with sand, gravel and other stones of the moraine.
The retreat, or the reduction of diluvian glaciers, did not operate in a sudden manner.
On the contrary, their period was to end much more slowly than it had begun.
During this retreat, the climate, ameliorating, did not have a uniform graduation, it was marked by oscillations as experienced today.
Years which were rather cold and wet even increased the volume of glaciers, which pushed back the little material dispersed during their decline.
It is these oscillations that produced the small moraines or erratic accumulations seen between those which, by their volume, indicate a new extension of the diluvian glaciers.
During the diminution of the glaciers that occupied the basins of southern Switzerland, separations took place, in several places, between the parts occupying the basins and those in the upper parts of the valleys of the Alps.
After this separation the fusion of parts of the plain took place in a manner even more unequal than before.
The torrents descending from the higher glaciers, having acquired some heat before reaching the basin of Lake Leman, accelerated the melting of the ice in the basin, and gave a propulsive force to the part situated to the north of the basin which was bathed by the waters.
It is as a result of this movement that the moraine of the second glacial extension is found between Lausanne and Geneva, in many places, especially below the height reached by the glacier at its maximum.
In other places, it is the glaciers of the last extension which have penetrated the preceding moraine in a lower region.
The great moraine of the second glacial extension on which is the hamlet of Plan-Cudrey near Villeneuve, can be assimilated to this case.
The materials disseminated at that time were pushed back by the glacier of a later time, which was formed again in the upper valley of the Tiniere.
Another phenomenon is also presented, it is that during the reduction or the time of a new glacial epoch, a glacier was pressing heavily against the mouth of one side stream, and that for several days the water could not
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penetrate into the mass; it finally flowed, for a few moments and over a greater or lesser extent, along the edge of the glacier and formed with the piled up masses an inclined plane between the glacier and the mountain which, after the disappearance of the glacier, was converted into a terrace.
But, if after such a great decline, the glacier by an oscillation intercepted the path of the stream, it would give rise to another ramp, which would then become a terrace such as can be seen above Orsières.
Downstream of the three current glaciers which in the Valsorine reunite as one, if the glacier were to melt, the moraine would fall and would form a talus from the small gravel plain located on the right which, in this case, would become a terrace.
The facts presented so far seem to prove by evidence the hypothesis that admits of many diluvial glacial epochs, from which was derived the formation of the quaternary terrains of Switzerland.
Geologists, adopting the glacial theory, are of the same opinion, but it is not true of those who live in other countries.
Since the appearance of the essay on the glaciers, two books have been published.
The authors divide the quaternary into several categories, which they attribute to causes of different natures.
One of the essays referred to in § 12, of MM. Charles Martin and B. Gastoldi, divides the superficial terrains of the Po valley into aqueous and glacial formations, comprehending in the former ancient moraines and glacial terrain; in the second the fossil-free alpine drift; of the Pliocene alluviums and the marine strata that support them they assign the aqueous formation to a geological era earlier than the period of ancient glaciers.
The other book entitled: Mémoire sur les phénomènes de la Suisse, Mr. Em. Desor, establishes, according to what he says in § 13, a difference between the erratic phenomena of Scandinavia and those of the Alps by attributing them to three different epochs.
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MM. Charles Martin and Gastoldi, after describing the moraines at the bottom of the Aosta Valley, said:
"Like the moraines of Rivoli, these repose on the alpine drift superimposed itself on Pliocene marine sands of the Po Valley.
The scattered glacial terrain, or deep superficial moraines joined together forms a narrow zone around the terminal moraine and it extends particularly throughout the region known as Bessa, where the glacier has deposited many 'erratic blocks.'
We see at the ravine of the Bériana, which descends from the wetlands of San Giovani, that the dispersed glacial terrain supports the superficial moraine and merges with the alpine drift which lies beneath it on the marine pliocene.
This area is less extensive than those around the moraine of the glacier of the valley at Susa."
Later they continue, saying:
"When one leaves the spread out glacial terrain which surrounds the moraines of Ivrea and Rivoli, to get to the Po, one no longer sees any vestige of striated rock, striped pebbles or erratic blocks.
It is thus evident that there are, in this space, no obvious traces at all that can show us the duration of an ancient glacier.
But as soon as we have crossed the Po to the foot of the hill that rises on the right bank, we see piles of stones which come from the part of the Alps in front of the erratic blocks from the same origin of glacial loam or mud."
After giving a description of the geological and mineralogical structure of the hill of Turin, which is forty feet high above the plain, 600 meters above the sea, they continue thus:
"The whole hill of Turin, the reverse side of the Alps, as well as the opposite side, all the heights, such as Superga, the Tour du Pin, telegraph stations today, the Hermitage (eremo) and the Madelaine, also the perimeter of the base, are dotted with erratic blocks."
They then give a picture of Serra and other localities and claim that the origin of the glacial drift is purely aqueous, like that of the Seine and the Loire which are deposited in the valleys, where, according to them, no glacier ever reached, even at the time of their greatest extension.
The alpine drift, from their point of view, is anterior to the glacial period and
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perhaps has no direct relationship with it. One may admit on this subject the very plausible explanation of Mr. Lecoy. *)
According to this geologist, a number of years of abundant fog and rain preceded and prepared for the age of the extension of the glaciers.
The alpine drift would thus belong to that geological era, however we can not consider it as synchronous to that of western France, as it contains no fossils, but one of our basins contains them.
In the parallel between the superficial terrains of the Po Valley basin and those of the Swiss basin, these gentlemen say that the old Piedmont glaciers have deposited at the mouths of the mighty alpine valleys moraines which by their height, their regularity, their symmetry show a centuries old location of glaciers at the same point, while in Switzerland, at least in the southern part of the basin, we see nothing like it.
To resolve this difference, they imagine that the Rhone glacier in its greatest extension, passed the Jura only to retreat at once and remain stationary a long time on the eastern side of the chain.
Here is their opinion:
"The southern slopes of the Alps are warmer than the northern slopes, the extended stationary period of the ancient glacier did not take place on the hill of Turin, but in the plain. Also during the long period of substantially invariable temperature during which the Rhone glacier reached to Jura, the glacier of the two Doires was in the middle of the plain, half way between the Alps and the hill; and during the period of maximum extension during which the Rhone glacier passed beyond the Jura, those of Aosta and of Rivoli reached the hill of Turin."
From the excerpts above, from the 'essai sur les terrains superficiels de la vallée du Pô', we can, with the exception of marine pliocene sands of which we shall speak boldly by-and-by, attribute the formation of the land to the various extensions of the glaciers of the diluvian epoch.
MM. Martin and Gastoldi themselves believe that the glacier in the Alps passed the top of the hill of Turin at the same time as the Rhone passed the Jura.
This extension is the one of the first epoch of which I spoke in § 20.
The glaciated terrain of the area of the Bessa and that of the foot of the hill of Turin, belong to that epoch.
*) Des glaciers et des climats, ou des causes atmosphériques en général.
(Glaciers and climate, or atmospheric causes in general.) 1847.
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The alpine alluvium situated between that area and the hill of Turin, to the second.
It is not surprising that between the glacial terrain of this first epoch around the moraines of Ivrea, of Rivoli and the Po, one meets with no trace of deep moraine or erratic blocks.
These gentlemen believe with good reason that as a glacier advances in the valley, it carries along its deep moraine.
During the first extension, this area was deeply excavated by the glacier.
The scattered terrain coming from the melting of the first glacier could not acheive this depth except by the oscillation that has formed the area of the Bessa.
It must therefore have been covered by the glacial alluvium of the second extension that has filled that excavation.
The lower end of a glacier often slides on the deposit formed by the stream issuing from under the ice.
The frontal moraine of Ivrea could therefore be deposited on the drift of the second ice age.
The superficial terrains of the Po Valley, overlaying the pliocene, can be attributed to the cause that produced the separate extensions of the ancient glaciers.
We now attempt to arrive at the same result as regards the erratic phenomenae of northern Europe and America that Mr. Desor attributed to several major phases or very marked epochs *), while in Switzerland, on the contrary , we are accustomed, according to him, to consider the erratic phenomena as the work of a single agent (either a current or a vast glacier), which would all in one go, polish the rocks , pile up the boulders, and transport the erratic blocks to their current position.
We have seen further back that in Switzerland also the erratic terrain belongs to several epochs.
One can therefore reply to his charge against us:
1. He has admitted too hastily that the same actions had to occur in northern Europe where, as in Switzerland, the surface of the ground is strewn with erratic blocks.
2. He has, as opposed to the simple laws of nature and the means that it uses, adopted more than one agent for the production of these phenomenae, but does not explain them.
*) See § 3 of this Memoir.
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Mr. Desor admits however, that as for the polished rocks, and roches moutonnées and striated rocks of Scandinavia, they are in all respects similar to those of Switzerland.
The erratic blocks are also foreigners and the elongated hills of sand and gravel, called Ozars, show in their external form an analogy with the moraines of glaciers, but they are stratified.
"It is true", he says, "that this stratification is often obscure, sometimes completely erased, but it suffices that it be distinct on a single point of the Osar to exclude any idea of glacial formation."
The Osar of Upsala, in this respect is even more significant since we found at the base marine shells, carried in a fine clay, indicating with evidence a slow and stable deposit.
However, this clay is topped by a layer of sand and gravel, so it must be admitted that these layers were deposited later, in other words, there was a succession of deposits, which is contrary to the idea of moraine which assumes that the entire mass was transported in a single piece.
Nowadays, all geologists agree that the Osars are sprinkled with erratic blocks, scattered in a greater or lesser quantity at their summits, and they must have been deposited in the latter locality.
This issue resolved, it follows that the transport of these blocks can not be, as in Switzerland, contemporary with the phenomenon produced by the scraping and polishing of rocks, and the transportation of the blocks is a simultaneous phenomenon; and therefore the blocks on top of the Osars have nothing in common with the blocks sometimes crowning our Swiss moraines.
The same reasoning can also be applied to the deposits of sand and gravel that cover a great part of the plains of Scandinavia and of northern Germany.
According to the glacial theory, we should naturally consider them as representing the deep moraine or layer of mud of a great Scandinavian glacier.
But the difficulty becomes real, when erratic deposits contain fossil remains.
Yet the erratic of Scandinavia contains a fair amount on several points and to a considerable height *), and as these are exclusively marine fossils, one is inevitably led to the conclusion that the deposits containing them must have been deposited, or at least shaped, by the waters, and that, therefore, Scandinavia was covered by the sea to the height where one can find marine shells.
*) Up to 600 feet, according to M. de Kilhau.
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As to the objection that could be made to me, that fossils are often mutilated and thus could be found there in this altered state, I need only point out that there exist near to Udegalla undeniable proofs of the presence of the sea in the barnacles that Mr. Brongniart found attached to the surface of the rocks above the sea at an elevation of 200 feet and that one sees near Christiania serpulae adhering to the polished rock at 170 feet above the fiord.
With regard to the deposits of Scandinavia and northern Germany containing marine fossil debris, Mr. Desor had to conclude that Scandinavia was covered by the sea to the height where there are marine shells.
We should be surprised that the author of the memoir did not indicate other vestiges of the elevation of this sea
If the land, containing such deposits, had been raised only 180 feet, the uplift would have left a legacy of faults produced between lands that remained in place and those that experienced this elevation.
If it was the sea which rose to such heights, it must have left traces of its shores over a vast extent.
It thus seems more natural to assume that (the first extension of the diluvian glaciers being still as unknown in northern Germany as that around the Alps) of the glaciers of the second extension, the one that crossed the basin of the Baltic Sea brought with it the sand, gravel and shells that it had broken and, in retreating as at the foot of the Jura, it formed the moraine on higher ground.
The erratic blocks common in these regions support the assumption of this first extension of the glaciers, because the sea could not fetch blocks large enough to make basins such as that of granite which is found in Berlin and which was made from an erratic block found in the country.
To the assumption that the deposits of sand and gravel of Scandinavia are deep moraines, Mr. Desor argues the existence of barnacles near Udegalla and of serpulae adhering to the polished rock near Christiania.
But these facts and the Osars around Stockholm and Upsala, can they not be attributed to the time of the third extension of the diluvian glaciers?
To be convinced, one should examine the localities that surround the three channels by which the Baltic Sea communicates with the ocean.
If on their left, and at very little distance, the land is over 60 meters above sea level, it seems likely that a glacier
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descending mountains to the right, has blocked the three arms and held back the waters of the Baltic to the height where there are barnacles near Udegalla.
The murky waters from the mountains produced then in the raised waters of the Baltic Sea a deposit of fine clay onto which molluscs found their way.
The edge of a glacier, then arriving at the place where one finds the Osar, covered the deposit of sand and gravel by increasing or crowning them with erratic blocks.
It will be for geologists, who will examine the localities, to recognize if the Osars were formed during the stationary times of the glacier or as a result of oscillation during retreat, or by another local circumstances, which gave them a particular form.
The explanations I have given on the formation of these terrains, are merely conjectures. Still it seems to me easier to account for these diverse phenomenae, by assuming the hypothesis of multiple glacial extensions, than add to the agent which formed roches moutonnés and the striated and polished rocks other agents that might have formed the Osars and transported the superficial blocks which terminate them, agents for which we can indicate neither the cause nor the mode of action. *)
It will be the same for the quaternary terrains of North America, where the appearance of the country, according to Mr. Desor, is indeed such that one can not ignore the action of erratic agents.
Although it is certain that the great diluvian formation, known as Drift, containing a quantity of striated pebbles in several localities, belongs, like the clay deposits containing shells on the banks of the St. Lawrence and Lake Champlein, to the Quaternary period, the striated pebbles should not, from my point of view, cease to be a sure sign that the deposits which contain them are of glacial origin, although the same species of shells have been discovered in very coarse deposits containing a large quantity of striated pebbles among others at Brocklyn near to New York.
They provide, on the contrary, evidence that these sedimentary deposits are a result of the extension of a diluvial glacier which, intercepting the flow of inland seas and lakes by meeting with hills of rock or mountains, has constrained the waters to spread out over large areas of land.
*) To properly understand the following, the proceedings of the Swiss Society meeting in Sion should be read.
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The vast deposits which in New England and Lower Canada are designated Cours - Drift or Drift grossier rise to a considerable height (up to 720 meters in the mountains of Vermont) and probably belong to the fourth extension of the diluvian glaciers.
The description of the quaternary terrains, given by M. Desor, provides no clue that indicates to me a way to place moraines in the first and second glacial extension, I assume that most can be attributed to the third, and that the definition of the Laurentide and Algonquin terrain, may be modified as follows:
A sedimentary terrain containing marine or lake fossils, posterior to the phenomenon of polishing of rocks, and anterior to the Drift of the 4th extension of diluvian glaciers.
By considering in this way the formation of the quaternary terrain of America, one accounts for the distribution of erratic blocks without having recourse to any agent other than the repeated extension of diluvian glaciers.
But what is the cause of these different extensions?
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