Edward S. (Edward Samuel) Farrow.

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330 A. C, Ramsay on the Olacial origin of certain Lakes

sloping valley or gorge, but (excepting little Bwallow-holes) it
cannot form and deepen a profound hollow, so as to leave a
rocky barrier all round : though it may fill with sediment one
that had previously been formed.

Thirdly, neither do most of the Swiss lakes lie in lines of dis-
location. For many reasons, I do not believe that any one of
them among the high Alps or on their flanks can be proved to
lie in lines of mere gaping firacture. Let us consider the nature
of such fractures.

In any country where the strata are comparatively little dis-
turbed and lie nearly horizonlally, if it be faulted, there is no
reason why the fractures should be open. In the Oolites, for
example, in the south of England, where &ults are numerous,
and in the New Bed Sandstone of the central counties, there is
generally a simple displacement of the strata up or down, on
one side or the other ; or, if the disturbance go beyond this,
it is that along the sloping line of fracture the beds on the
downthrow side are turned up, and those on the opposite side
bent down, by pressure and slipping combined. In more dis-
turbed districts, like the Welsh Coal-measures, the same phe-
nomena are observable: witness, for instance, the numerous
sections firom accurate observation, drawn on a true scale, by
Sir Henry De la Beche, Sir William Logan, and others. Ex-
perience, both above ground and in mines, proves the same.
Most lodes are in fractures, and many lie in lines of fault. In
metamorphic, excessively contorted, and greatly firactured dis-
tricts, like those of Devon, Cornwall, and Wales, the cracks,
whether bearing metals or not, vary from mere threads to a few
&thoms in widtn. They are always filled with quartz or other
foreign substances, frequently harder than the surrounding ma-
trix. I have often traced lodes on the surface, in Wales, by the
hard matter filling the crack standing in relief above the surface
of the softer enclosing rock. In limestone rocks the cracks are
usually partly filled with crystallized carbonate of lime. Lines
of fracture are not, therefore, for purposes of denudation, neces-
sarily lines of weakness, unless it happen that on opposite sides
of the fault hard and soft rocks come together, when of course
the softer rocks will wear away more rapidly, and generally
originate a straight valley.

Again, in an excessively contorted country, such as the AIpa>
it is, I believe, impossible, in consequence of tJiat contortion^ that
there should be gaping fractures now exposed to view. Assum-
ing for the sake of argument the sudden violent contortion of
the strata of any great tract of country, we shall see that the
contorted rocks now exposed at the surface^ even if broken, would
be most unlikely to gape.

The expression "elevation of mountains" conveys to the minds

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in Europe and North Ameriqa. 881

of many persons the idea that the elevation has been produeed
by some force acting from below, along a line in the case of a
chain, and on a point of greater or less extent when the moun-
tains lie in a cluster, as a whole, more or less dome-shaped.
Such forces would stretch the strata ; and, when they could no
longer stand the tension, cracks would ensue, and many lines of
valley are assumed to lie in such fracture& But in Wales, the
Highlands of Scotland, and more notably in the Alps, the strata
now visible have been compressed and crumpled, not stretched,
and they occupy a smaller horizontal space than they did pre-
vious to the formation of the chain.

Let us supoose a set of strata of (s^) 14,000 to 20,000 feet
in thickness, like the rodcs of North Wales, and let these be
spread out horizontally over thousands of square miles. Let
these strata, from any cause, be compressed from the right and
left so as to be contorted, and occupy a smaller horizontal area
than they did before disturbance. Then, at a great depth, where
the superincumbent strata pressed heavily on the lower beds,
the latter would be crumpled up, cleavage would often supervene,
and gaping fractures would be impossible; for, where mere fitic-
tures occurred, the walls of the cracks would be pressed more
closely together. But nearer the surface, where tnere was less
weight, and at it, where there was none, the beds would extend
into larger curvei3 than they did lower down ; and where the
limits of extensibility were passed, shattering might take place,
and yawning chasms might ensue. In all violently contorted
countries, however, as in the cleaved rocks of North Wales, for
instance, the present surface shows those originally deep-seated
contortions that since disturbance have been exposed by denuda-
tion ; otherwise the rocks would not be cleaveo. I therefore do
not believe that in any country I have seen, such as Wales or
Switzerland, there are any lakes now occupying yawning frac-
tures, consequent in Switzerland on Post-eocene or Post-miooene
disturbances. On the contrary, they Jie in hollows of denuda-
tion, shortly to be explained, of later date than these disturb-

Fourthly, again, it may be supposed that the great lakes lie
each in an area of special subsidence ; but, in reply to this, it is
evident that among the unnumbered lakes of Switzerland and
Italian Alps it would be easy to show a gradation in size, from
the smallest tarn that lies in a rock-basin to the Lakes of Geneva
and Constance. Neither do I see any reason why mere size
should be considered the test of subsidence. Disallowing that
test, we should require a ffreat number of special subsidences,
each in the form of a rock-basin, in contiguous areas. Between
the Seidelhom and Thun, for example, we should require one
for the Todten See, several on the plateau on the north imme-

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383 A. C. Ramsay on the Glacial origin of certain Laies

diatelj under the Seidelhom, one for the lake at the Grimael/
another for the drained lake at the Kirchet/ and another for
the lakes of Brienz and Thun. In Sutherlandsbire these areaa
of special subsidence would be required by the hundred, and m
North America by the thousand.

Signor Gastaldi, in a masterly memoir on the composition of
the Miocene conglomerates of riedmont,* considers with reason
that the large angular blocks of these strata, many of them fer-
transported, and some of them foreign to the Alps and Apen-
nines, have been deposited from ice-rafts; and thence he infers
the existence of glaciers during a part of the Miocene epodi^
But, admitting this, it is evident that the distribution of the
Post-pliocene glaciers of the Alps must, in all details, have been
quite different from those of Miocene age, in consequence of the
great disturbance that the Alpine rocks underwent after the close
of the Miocene epoch, and the subsequent formation of numerous
new valleys of denudation. Traces of the long lapse of time
between the Miocene and the later Glacial epoch are in other
countries but imperfectly preserved in the subdivisions of the
Crag, and of other minor formations of still later date. Of the
finer gradations that unite these subdivisions, few traces have
been described. For long before, and during all these Crag
epochs and the ages between them, of which we have little trace,
and during all the time that elapsed from the close of the Ciug
until the period of extreme cold came into action, the Alps stood
above the sea, and suffering subaerial denudation, valleys were
being formed and deepened. It is possible that, while the mild
climates of the Lower Crag epochs endured, there may still have
been glaciers in the higher Alps ; but at whatever period the
later glaciers commenced, those who allow the extreme slowness
of geological change will admit that the period was immense
that elapsed during the gradual increase of the glaciers, until,
in an epoch of intensest cold, the ice abutted on the Jura in one
direction, in another spread far beyond the present area of the
Lake of Constance, ana on the south invaded the plains of IxMn-
bardy and Piedmont. During all that time, weather and running
water were at work modifying the form of the ground under
review. But, as I have alreadv explained, these two agents
were incapable of scooping out deep nollows surrounded on all
sides by rocks, and it therefore follows that the lakes first ap-
peared aft;er the decline of the glaciers left the surface of the
country exposed approximately as we now see it, — unless we
admit, what seems to me impossible, that fractures, formed at
the close of the Miocene epocn, remained filled wtth water until

' See the " Old Glaciers of Switzerland and North Wales."
^ ** Sugli elementi che compoogoDO i conglomerati MiooeDi del Piemonte,** ToriD,

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in Europe and North America. 888

the great glaciers filled them with ice; or believe, with De Mor-
tillet, that the valleys and lake-hollows were charged with water-
borne alluvial or diluvial dSbris before the glaciers ploughed it

Allowing the hypothesis of De Mortillet, the rock-basins must
have been twice tilled with water; but, according to my hypo-
thesis, they did not exist as lakes till after the disappearance of
the glaciers.

But the glacier map of ancient Switzerland shows that the
areas now occupied by the great lakes, both north and south of
the Alps, have all been covered with glaciers. No Tertiary de-
posit, of an age between the close of the Miocene and the com-
mencement of the Glacial epoch, lies between the Alps and the
Jura ; and, had the hollows of the lakes existed prior to the
great Glacial epoch, we ought, but for some powerful wasting
agent, probably in these hollows, still to find some traces of fresh
water deposits, perhaps of the age of part of the Crag. No such
relics exist

The Oreat Lakes. Lake of Geneva, — The Lake of Geneva is
about 46 miles in length by about 12 in breadth, and its delta,
once part of the lake, between Villeneuve and Bex, is 12 miles
long. The latter and a small part of the banks of the lake be-
yond the mouth of the river lie in the great Khone valley, formed
of older Tertiary and Secondary rocks. All the rest of the lake
is surrounded by the low country formed of the various subdi-
visions of the Molasse and Nagelfiuh. The lake is 1280 feet
above the level of the sea, and 984 feet deep towards the eastern
end, according to the sounding of De la Beche.*

Geneva itself stands on superficial c?^&m ; but the solid rock
first appears in the river-bea below Geneva, at Vernier, at the
level or 1197 feet above the sea — onlv 83 feet below the surface
of the l^e, or 951 feet above the aeepest part of its bottom.
Any one acquainted with the remainaer of the physical geo-
graphv of the country will therefore see that the water of the
mke lies in a true rock-basin. The question thus arises. How
was this basin formed ?

1st. It does not lie in a simple synclinal basin ; for, though
the Lake of Geneva lies in the great synclinal hollow of the
Miocene strata between the Alps and the Jura, it is evident by
an inspection of the country that the flexures of that formation
are of far greater antiquity than the lake. These flexures have

• See an admirable memoir hj G. de Mortillet, ** Des Anciens Glaciers du Ver-
aant Italien des Alpes.** Milan, 1860. Though I had seen his map, I had not teen
this memoir when I read my paper ; and the passages in which it is mentioned
have been added as these pages pass through the pre^. His theory leaves the
difficulty of the first formations of the basins untoucned, unless we belieye (which
I do not) that the Alpine Talleys are lines of fracture.

* Edinburgh Philosophical Journal, 1820, ii, 107, and plate 2.

Am. Joub. Sci.— Second Skbiss, Vol. XXXV, No. 106.— Mat, 1868.

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aM A. C, Ramtay an the Qlacial origin of certain Lakes

been denuded, and the lake runs in a great degree across their

2nd. For reasons already stated, it is, I believe, impossible to
prove that the lake lies in an area of special subsidence, all the
probabilities being against this hypothesis.

8rd. It is almost needless to say that the Lake of Geneva is
too wide to lie in a mere line of fracture ; and I know of no
reason why the valley of the Ehone, where occupied by the
delta, should be esteemed a line of fault or gaping fissure, anv
more than many other valleys in Switzerland, which many geol-
ogists will consider with me chiefly the result of the old and
long-continued subaerial denudation of highly disturbed strata.
I could enter on details to prove this point, but they belong
rather to the rock-geology of Switzerlana than to the matter in

4th. Those who do not believe in the existence and excavating
power of great and sudden cataclysmal floods will at once see
that the area of the lake cannot be one of mere watery erosion;
for not ordinary running water, and fer less the still water of a
deep lake, can scoop out a hollow nearly 1000 feet in depth.

Now, if the lake of Geneva do not He in a synclinal trough,
in an area of subsidence, in a line of fracture, or in an area of
mere aqueous erosion, we have only one other great moulding
agency left by which to modify the form of the ground, namely,
l£at of ice.

When at its largest, the great clacier of the Ehone debouched
upon the Miocene beds where the eastern end of the Lake of
Geneva now lies. The boulders on the Jura, near NeuchStel,
prove that this glacier was about 2200 feet thick where it abut-
ted on the mountains ; and, where it first flowed out upon the
plain at the mouth of the valley of the Ehone, the ice, according
to Charpentier, must have been at least 2780 feet thick." Add
to this the depth of the lake, 984 feet, and the total thickness of
the ice must have been about 3764 feet at what is now the east-
ern part of the lake. I conceive, then, that this enormous
mass of ice, pushing first northwest and then partly west,
scooped out the hollow of the Lake of Geneva most deeply in
its eastern part opposite Lausanne, where the thickness and
weight of ice, and consequently its grinding power, were greatest
This weight, decreasing as it flowed towanls the west, from the
natural diminution of the glacier, possessed a diminishing ero-
ding power, so that less matter was planed out in that direction,
and thus a long rock-basin was formed, into which the waters of
the Ehone and other streams flowed when the climate ameliorate
and the glacier retired.

»• The Lake of Gh^neva is 197 feet lower than tho Lake of Neuch&tel. The

Slader first surmonnted the hills between Lausanne and Vcvay, and then flowed
own the general slope northwards to the Jura.

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• in Europe and North Amaica. 885

Lake of Neuchdtd. — ^The basins of the lakes of Nenchfitel,
Bienne, and Morat were, I consider, hollowed out in a similar
manner, diflFering in points of detail. Near the Lake of Neu-
ch£tel, on the flank of the Jura, the fan-shaped end of the Bhone
glacier attained its greatest height, swellea in size and pressed
on as it was by others that descended from the north snow-
shed of the mountains between the Oldenhorn and the great
snow-fleld above Grindelwald. According to estimates based
on the highest ice-stranded boulders, the ice rose 2203 feet
above the present surface of the lake. The lake is now 1427
feet above the sea, and 480 feet deep ; and the Lake of Bienne
is 1425 feet above the sea, and 281 feet in depth. The bottom
of the Lake of Neuch&tel is thus 947 feet above the sea. Unless
the gravel, therefore, on the banks of the Aar, immediately east
of the latter, be over 480 feet deep, the hollow of the lake near
its immediate bounds is a true rock-basin; for on the north,
south, and west it is surrounded by solid Secondary and Miocene
rocks. Even if the rock does not rise close to the surface in the
river near the lake, still, at Solothurn, strata in place come close
to the river-bank on both sides, the river being 1414 feet above
the sea. Under any circumstances there must therefore be a
long, deep trough between Solothurn and the rocks a little
southwest of the Lake of Neuchfitel. How was this basin
formed? When the glacier, debouching fh)m the valley of the
Bhone, spread out like a fan and pressed forward till it abutted
on the Jura, its onward progress was stopped b^ that mountain ;
and direct further advance being hinderea, the ice spread north-
east and southwest, to the right and left, and being as a^^hole
thickest and heaviest above the area where the lake now lies, a
greater quantity of the Miocene strata on which it rested must
have been ploughed out there than further on towards the north-
east and southwest ends of the glacier, towards which the ice,
gradually declining in thickness, exercised less grinding power.
In this manner I believe 'the troughs were formed in which lie
the three lakes near Neuchfitel ; and when the ice finally re-
treated, the ordinary drainage of the country* filled them with
water, the clifls on tte southeastern side of the Lake of Neu-
chStel and other changes of the form of the ground having since
been produced or modified by watery erosion and the l(^al de-
position of silt and alluvial gravel.

The Lake of Thun.— The Lake of Thun is 1825 feet above the
sea, and 776 feet deep. Its bottom is therefore 1049 feet above
the sea. It is about 10 miles in length, 1-^ broad, and its length
chiefly cuts across the strike of rocks of Secondary and Miocene
age. The Lake of Brienz (about the same size) is more remark-
able ; for, while its level is 1850 feet above the sea, its depth is
more than 2000 feet; so that its bottom is at least between 100

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8S6 A. C. Ramsay on the Olacial origin of certain Lakes

and 200 feet below the level of the sea. Before the fonnation
of the alluvial plain between, these two lakes were probably
united ; and whether or not this was the case, it is evident, from
its great depth, that the Lake of Brienz lies in a true rock-basin.
Even if below Thun the rocks do not crop nearer than Solothum,
the Lake of Thun still lies in a rocky hollow more than 600 feet
deep, both hollows having, I believe, been deepened by the ^reat
old glacier of the Aar, the ice of which was so thick, that above
Brienz it overflowed into the valley of Sarnen by the Brunig,
about 1460 feet above the Aar below Meyringen, and sent off
a branch which scooped out the hollows of the Lakes of Lun-
gern and of Sarnen on its course towards Alpnach on the Lake
of Lucerne.

The Lake of Zug. — The Lake of Zug is about 9 miles long,
from 1 to 2^ wide, 1861 feet above the sea, and 1279 feet deep ;
and its bottom is therefore only 82 feet above the sea. The
whole is surrounded by Miocene strata, the strike of which the
lake cuts across, and its great depth clearly shows that it lies in
a rock-basin.

The Lake of Lucerne, — The Lake of the Four Cantons (Lucerne)
ramifies among the mountains and extends its arms in various
directions. In its lower part, the branches that run N.E. to
Kussnach and S. W. towaras Gestad lie partly in the strike of the
Miocene and older strata ; but for the most part it runs across
the average strike of the Eocene and Secondary rocks, between
banks, sometimes precipitous, that rise in noble cliffs sometimes
more than 2000 feet above the water. Its height is 1428 feet
abov^ the sea, and its recorded depth 858 feet ; but the shape of
the banks and the round number of 800 French feet make it
likely that it may contain deeper gulfs than have yet been
plumbed. If not, then its bottom is 575 feet above the sea ; and
those acquainted with the shape of the ground by Lucerne will
easily be convinced that the lake lies in an actual rock-basin.
The steepness of the walls of this lakd more resembles the sides
of a rent than those of any of the basins yet described, and the
re-entering angles of rock opposite curving bays have been cited
as evidences of fracture, one side being supposed to fit into
the other. Bui in most cliffy valleys of aqueous erosion there
are necessarily such reentering angles, from the common action
of running water ; and, in Switzerland, ere these valleys were
filled with ice, they existed in some shape, and were drained by
rivers that deepened them and ^ve them a general form pre-

Saratory to the flow of the ice that largely modified their out-
nes. I should no more consider the re-entering angles a sign
of gaping fracture in these valleys than I would the bends of the
Welsh valleys or of the tortuous Moselle. But even if at first
sight jone were inclined to believe the space between the oppo-

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in Europe and North America. SOT

site clii& between Bronnen and Fliihlen to be an open fracture,
if we take a moderate average slope for each side, say of 65°,
and produce it below the water, we get a depth, ere the lines
meet, of between 7000 and 8000 feet — a very improbable
depth for the original hollow of the lake. But it may be said
that the fracture has been much widened by degradation, the
line of the break merely giving a line of weakness, along which
the surface-drainage might widen the valley. If, however, we
only take an angle for the sides of the lake giving a moderate
depth, the necessity for a fracture does not exist, and we recur to
some process of mere erosion for the scooping of the hollow in
which the water lies, that process having, I consider, been the
loM-continued grinding of the ice of the great glacier.

The Lake of Zurich, — The Lake of Zurich runs from N.W. to
S.E., across the average strike of the Miocene strata, which are
much disturbed towards its eastern end. It is bounded by hi^h
hills, much scarred by the weather, on which the different Mio-
cene strata often stand out in saccessive horizontal steps. The
linth Canal and the Wallen See lie in an eastern prolongation
of this valley, which is still further extended to the vallev of the
Tipper Bhine at Sarins. The lake is about 25 English miles
in length, b;;^ 2i wide in its broadest part. A great moraine
partlv dams it up at its outflow at Zuricn ; and a second forms
the snallow at Eapperswyl, where the lake is crossed by a long
wooden bridge. The general level of the water is 1841 feet
above the sea, and only about 689 deep ; and the bottom of the
lake is therefore 702 feet above the sea. The limestone rocks
at Baden, on the Limat, are 1226 feet above the sea ; and the
lake therefore lies in a true rock-basin, though it is probable
that the old moraine at Zurich accounts for the retention of the
water of the lake at its precise level. The long hollow was in
old times entirely fiUed by the great glacier which descended
from the mountains between the Todi and the Trinserhom,
through the valley of the Linth, to Baden.

Tlie Wallen See. — The Wallen See lies in a deep valley, whose
ciiSv slopes of Secondary rocks rise from 2000 to 8000 feet, and
in the Leistkamm 4500 leet above the surface of the lake. The
lake itself is 1891 feet above the sea ; and from the great steep-
ness of its banks it may be inferred that it is exceedingly deep,
but none of the authorities I have consulted give its sounding.
A large branch from the great Bhine glacier joined that at uie
vallev of Glarus and Zurich through this wide gorge, and ground
out the hollow of the Wallen See.

The Lake of Constance. — The Lake of Constance, the largest
sheet of water in Switzerland, is about 50 miles in length, by
about 16 in breadth at its broadest part It is entirely sur-
rounded by Miocene strata, often considerably disturbed, and

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888 A. C. Ramsay on the Glacial origin of certain Lakes

formiDg great bills towards the S.E., which in a remarkable
manner evince all the signs of long-continued erosion by run-
ning water, conveying the impression that chiefly by that means
all the deep valleys of the district have been worn since the
close of the Miocene epoch. This lake lies 1298 feet above the
sea; and, its depth being 912 feet^' its bottom is only 386 feet
above the sea. The falls of the Rhine are 1247 feet above the
sea; and the lake therefore lies in an unmistakable rock-basin,
the whole of which was once overflowed by the deep and broad-
spreading glacier of the Upper Ehine valleys which stretched
far northward beyond the lake into Baden and Wurtemberg.
Being of greatest thickness where it entered the region of the
lake, by its enormous weight and grinding power it scooped out,
in the soft rocks below, the wide hollow now filled with water.

Online LibraryEdward S. (Edward Samuel) FarrowThe American journal of science and arts → online text (page 43 of 61)