James Croll.

Climate and time in their geological relations: a theory of secular changes ... online

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striations than produce them.

A floating berg moves with great steadiness ; but a berg
that has run aground cannot advance with a steady motion.
If the rock over which the berg moves offers little resistance, it
may do so ; but in such a case the berg could produce but little
effect on the rock.

Dr. Sutherland, who has had good opportunities to witness the
effects of icebergs, makes some most judicious remarks on the
subject. " It will be well " he says, " to bear in mind that
when an iceberg touches the ground^ if that ground he hard and
resisting, it mmt come to a stand, and the propelling power con-
tinuing, a slight leaning over in the water, or yielding motion
of the whole mass, may compensate readily for being so sud-
denly arrested. If, however, the groimd be soft, so as not to
arrest the motion of the iceberg at once, a moraine will be the
result ; but the moraine thus raised will tend to bring it to a
stand." {

There is another cause referred to by Professor Dana, which,
to a great extent, must prevent the iceberg from having an
opportunity of striating the sea-bottom, even though it were
otherwise well adapted for so doing. It is this : the bed of the

• Beport on Icebergs, read before the Association of American Geologists,
SilUman'a Joumaly vol. xliii., p. 163 (1842).
t " Manual of Geology/* p. 677.
X Quart. Joom. Geol Soc., yoL ix., p. 306.

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ocean in the track of icebergs must be pretty much covered with
stones and rubbish dropped from the melting bergs. And this
mass of rubbish will tend to protect the rock.* *

If icebergs cannot be shown a priori, from mechanical con-
siderations, to be well adapted for striating the sea-bottom^ one
would naturally expect, from the confident way in which it is
asserted that they are so adapted, that the fact has been at least
established by actual observation. But, strange as it may
appear, we seem to have little or no proof that icebergs actually
striate the bed of the ocean. This can be proved from the direct
testimony of the advocates of the iceberg theory themselves.

We shall take the testimony of Mr. Campbell, the author of
two well-known works in defence of the iceberg theory, viz.,
"Frost and Fire," and "A Short American Tramp." Mr.
Campbell went in the fall of the year 1864 to the coast of
Labrador, the Straits of Belle Isle, and the Gulf of St. Lawrence,
for the express purpose of witnessing the effects of icebergs,
and testing the theory which he had formed, that the ice-
markings of the glacial epoch were caused by floating ice and
not by land-ice, as is now generally believed.

The following is the result of his observations on the coast of

Hanly Harbour, Strait of Belle Isle:— "The water is 37^ F.
in July. ... As fast as one island of ice grounds and bursts,
another takes its place; and in winter the whole strait is
blocked up by a mass which swings bodily up and down,
grating along the bottom at all depths. . . . Examined the
beaches and rocks at the water-line, especially in sounds.
Found the rocks groimd smooth, but not striated, in the sounds "
(Short American Tramp, pp. 68, 107).

Cape Charles and Battle Harbour : — " But though these
harbours are all frozen every winter, the rocks at the water-Une
are not striated^* (p. 68).

At St. Francis Harbour : — " The water-line is much rubbed,
smooth, but not striated*^ (p. 72).

• Dana's «* Manual of Geology," p. 677.


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Cape Bluff: — "Watched the rocks with a telescope, and
failed to make out struB anywhere ; but the water-line is every-
where rubbed smooth " (p. 75).

Seal Islands : — **No strue are to be seen at the land-wash in
these sounds or on open sea-coasts near the present water-litie'*
(p. 76).

He only mentions having here found striatlons in the three
following places along the entire coast of Labrador visited by
him ; and in regard to two of these, it seems very doubtful that
the markings were made by modem icebergs.

Murray's Harbour: — "This harbour was blocked up with
ice on the 20th of July. The water-line is rubbed, and in some
places striated'* (p. 69).

Pack Island : — " The water-line in a narrow sound was
polished and striated in the direction of the sound, about
N.N.W. This seems to be fresh work done by heavy ice
drifting fix>m Sandwich Bay ; but, on the other hand, stages udth
their legs in the sea, and resting on these very rocks, are not stcept
away by the ice " (p. 96), If these markings were modem, why
did not the " heavy ice " remove the small fir poles supporting
the fishing-stages ?

Red Bay: — "Landed half-dressed, and found some stria)
perfectly fresh at the water-level, but weathered out a short
distance tw&nc?" (p. 107). The striations " inland " could not
have been made by modem icebergs ; and it does not follow
that because the markings at the water-level were not weathered
they were produced by modem ice.

These are the evidences which he found that icebergs striate
rocks, on a coast of which he says that, during the year he
visited it, " the winter-drift was one vast solid raft of floes and
bergs more than 160 miles wide, and perhaps 3,000 feet thick
at spots, driven by a whole current bodily over one definite
course, year after year, since this land was found " (p. 85).

But Mr. Campbell himself freely admits that the floating
ice which comes agroimd along the shores does not produce
striao. " It is sufiiciently evident," he says, " that glacial strice


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are not produced by thin bay ice " (p. 76). And in " Frost and
Fire," vol. ii., p. 237, he states that, " from a careful examina-
tion of the water-line at many spots, it appears that bay-ice
grinds rocks, but does not produce stnation"

" It is impossible," he continues, " to get at rocks over which
heavy icebergs now move ; but a mass 150 miles wide, perhaps
3,000 feet thick in some parts, and moving at the rate of a
mile an hour, or more, appears to be an engine amply sufficient
to account for stria) on rising rocks." And in "American
Tramp," p. 76, he says, " strice must be made in deep water by
the large masses which seem to pursue the even tenor of their
way in the steady current which flows down the coast."

Mr. Campbell, irom a careful examination of the sea-bottom
along the coast, finds that the small icebergs do not produce
strisD, but the large ones, which move over rocks impossible to
be got at, " must " produce them. They *' appear " to be amply
sufficient to do so. If the smaller bergs cannot striate the sea-
bottom, why must the larger ones do so P There is no reason
why the smaller bergs should not move as swiftly and exert as
much pressure on the sea-bottom as the larger ones. And even
supposing that they did not, one would expect that the light
bergs woidd eflfect on a smaller scale what the heavy ones would
do on a larger.

I have no doulft that when Mr. Campbell visited Labrador
he expected to find the sea-coast under the water-line striated
by means of icebergs, and was probably not a little surprised to
find that it actually was not. And I have no doubt that were
the sea-bottom in the tracks of the large icebergs elevated into
view, he woidd find to his surprise that it was free from stria-
tions also.

So far as observation is concerned, we have no grounds from
what Mr. Campbell witnessed to conclude that icebergs striate
the sea-bottom.

The testimony of Dr. Sutherland, who has had opportunities
of seeing the effects of icebergs in arctic regions, leads us to
the same conclusion. " Except," he says, " from the evidence


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afforded by plants and animals at tlie bottom, we have no meam
whatever to ascertain the effect produced by icebergs upon the
rocks.* In tbe Malegat and Waigat I have seen whole clus-
ters of these floating islands, drawing from 100 to 250
fathoms, moving to and fro with every return and recession of
the tides. I looked very earnestly for grooves and scratches
left by icebergs and glaciers in the rocks, but always failed to
discover any." t

We shall now see whether river-ice actually produces stria-
tions or not. If floating ice under any form can striate rocks,
one would expect that it ought to be done by river-ice, seeing
that such ice is obliged to follow one narrow definite track.

St. John's River, New Brunswick : — "This river," says Mr.
Campbell, " is obstructed by ice during five months of the year.
When the ice goes, there is wild work on the bank. Arrived .
at St. John, drove to the suspension-bridge. ... At this spot,
if anywhere in the world, river-ice ought to produce striation.
The whole drainage of a wide basin and one of the strongest
tides in the world, here work continually in one rock-groove ;
and in winter this water-power is armed with heavy ice. There
are no strim about the water-line." $

Eiver St. Lawrence : — " In winter the power of ice-floats
driven by water-power is tremendous. The river freezes and
packs ice till the flow of water is obstructed. The rock-pass
at Quebec is like the Narrows at St. John's, Newfoundland.
The whole pass, about a mile wide, was paved with great
broken slabs and round boulders of worn ice as big as small
stacks, piled and tossed, and heaped and scattered upon the

level water below and frozen solid This kind of ice

does NOT produce striation at the water-margin at Quebec. At
Montreal, when the river * goes,' the ice goes with it with a

vengeance The piers are not yet striated by river-ice at

Montreal The rocks at the high-water level have no

trace of glacial striae The rock at Ottawa is rubbed by

• Quart. JouTD. Geol. Soc, vol. ix., p. 306. f " Journal/' vol, i., p. 38.

J "Short American Tramp," pp. 168, 174.


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river-ice every spring, and ahcays in one direction^ hut it is not
striated, .... The surfaces are all rubbed smooth, and the
edges of broken beds are rounded where exposed to the ice ; but
there are no strimJ* *

When Sir Charles Lyell visited the St. Lawrence in 1842, at
Quebec he went along with Colonel Codrington "and searched
carefully below the city in the channel of the St. Lawrence, at
low water, near the shore, for the signs of glacial action at the
precise point where the chief pressure and friction of packed
ice are exerted every year," but found none.

" At the bridge above the Falls of Montmorenci, over which
a large quantity of ice passes every year, the gneiss is polished,
and kept perfectly free from lichens, but not more so than rocks
similarly situated at waterfalls in Scotland. In none of these
places were any long straight grooves observable." t

The only thing in the shape of modem ice-markings which
he seems to have met with in North America was a few straight
furrows half an inch broad in soft sandstone, at the base of a
oliff at Cape Blomidon in the Bay of Fundy, at a place where
during the preceding winter " packed *' ice 15 feet thick had
been pushed along when the tide rose over the sandstone

The very fact that a geologist so eminent as Sir Charles Lyell,
after having twice visited North America, and searched specially
for modem ice-markings, was able to find only two or three
scratches, upon a soft sandstone rock, which he could reasonably
attribute to floating ice, ought to have aroused the suspicion of
the advocates of the iceberg theory that they had really formed
too extravagant notions regarding the potency of floating ice
as a striating agent.

There is no reason to believe that the grooves and markings
noticed by M. Weibye and others on the Scandi^vian coast
and other parts of northern Europe were made by icebergs.

• *• Short American Tramp," pp. 239—241.
t ** Travela in North America," toL iL, p. 137.
X Ibid., voL ii., p. 174.


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Professor Geikie has clearly shown, from the character and
direction of the markings, that they are the production of land-
ice.* If the floating ice of the St. Lawrence and the icebergs
of Labrador are unable to striate and groove the rocks, it is not
likely that those of northern Europe will be able to do so.

It will not do for the advocates of the iceberg theory to as-
sume, as they have hitherto done, that, as a matter of course,
the sea-bottom is being striated and grooved by means of ice-
bergs. They must prove that. They must either show that, as
a matter of fact, icebergs are actually efficient agents in striating
the sea-bottom, or prove from mechanical principles that they
must be so. The question must be settled either by observation
or by reason ; mere opinion will not do.

The Amount of Material transported by Icebergs much exag-
gerated, — The transporting of boulders and rubbish, and not
the grinding and striating of rocks, is evidently the proper
function of the iceberg. But even in this respect I fear too
much has been attributed to it.

In reading the details of voyages in the arctic regions one
cannot help feeling surprised how seldom reference is made to
stones and rubbish being seen on icebergs. Arctic voyagers,
like other people, when they are alluding to the geological
effects of icebergs, speak of enormous quantities of stones being
transported by them ; but in reading the details of their voy-
ages, the impression conveyed is that icebergs with stones and
blocks of rock upon them are the exceptions. The greater
portion of the narratives of voyages in arctic regions consists
of interesting and detailed accounts of the voyager's adven-
tures among the ice. The general appearance of the icebergs,
their shape, their size, their height, their colour, are all noticed ;
but rarely is mention made of stones being seen. That the
greater number of icebergs have no stones or rubbish on them
is borne out by the positive evidence of geologists who have
had opportunities of seeing icebergs.

Mr. Campbell says: — "It is remarkable that up to this

• Proceedings of the Royal Society of Edinburgh, Session 1865 — 66, p. 537.


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time we have only seen a few doubtful stones on bergs which we

have passed Though no bergs with stones on them or in

them have been approached during this voyage, many on board

the Ariel have been close to bergs heavily laden A man

who has had some experience of ice has never seen a stone on a
berg in these latitudes. Captain Anderson, of the Eurqpa, who
is a geologist, has never seen a stone on a berg in crossing the
Atlantic. No stones were elearly seen on this trip J** Captain
Sir James Anderson (who has long boen familiar with geology,
has spent a considerable part of his life on the Atlantic, and has
been accustomed to view the iceberg as a geologist as well as a
seaman) has never seen a stone on an iceberg in the Atlantic.
This is rather a significant fact.

Sir Charles Lyell states that, when passing icebergs on the
Atlantic, he '* was most anxious to ascertain whether there was
any mud, stones, or fragments of rocks on any one of these
floating masses ; but after examining about forty of them with-
out perceiving any signs of frozen matter, I left the deck when
it was growing du8k."t After he had gone below, one was
said to be seen with something like stones upon it. Tho
captain and officers of the ship assured him that they had
never seen a stone upon a berg.

The following extract from Mr. Packard's " Memoir on the
Glacial Phenomena of Labrador and Maine,'* will show how
little is effected by the great masses of floating ice on the
Labrador coast either in the way of grinding and striating the
rocks, or of transporting stones, clay, and other materials.

"Upon this coast, which during tho summer of 1864 was
lined with a belt of floe-ice and bergs probably two hundred
miles broad, and which extended from the Gulf of St, Lawrence
at Belles Amours to the arctic seas, this immense body of
floating ice seemed directly to produce but little alteration in its
physical features. If we were to ascribe the grooving and
polishing of rocks to the action of floating ico-floes and bergs,

• " Short American Tramp/' pp. 77, 81, 111.
t " Second Visit," vol. ii., p. 367.


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how is it that the present shores far above (500), and at least
250 feet below, the water-line are often jagged and angular,
though constantly stopping the course of masses of ice impelled
four to six miles an hour by the joint action of tides, cur-
rents, and winds P No boulders, or gravel, or mud were seen
upon any of the bergs or masses of shore-ice. They had
dropped all burdens of this nature nearer their points of
detachment in the high arctic regions/' ....

" This huge area of floating ice, embracing so many thou-
sands of square miles, was of greater extent, and remained
longer upon the coast, in 1864, than for forty years previous.
It was not only pressed upon the coast by the normal action of
the Labrador and Greenland currents, which, in consequence of
the rotatory motion of the earth, tended to force the ice in a
south-westerly direction, but the presence of the ice caused the
constant passage of cooler currents of air from the sea over the
ice upon the heated land, giving rise during the present season
to a constant succession of north-easterly winds from March
imtil early in August, which further served to crowd the ice
into every harbour and recess upon the coast. It was the
universal complaint of the inhabitants that the easterly winds
were more prevalent, and the ice * held ' later in the harbours
this year than for many seasons previous. Thus the fisheries
were nearly a failure, and vegetation greatly retarded in its
development. But so far as polishing and striating the rocks,
depositing drift material, and thus modifying the contour of the
surface of the present coast, this modem mass of bergs and float-
ing ice effected comparatively little. Single icebergs, when
small enough, entered the harbours, and there stranding, soon
pounded to pieces upon the rocks, melted, and disappeared. From
Cape Harrison, in lat. 55°, to Caribo Island, was an interrupted
line of bergs stranded in 80 to 100 or more fathoms, often miles
apart, while others passed to the seaward down by the eastern
coast of Newfoundland, or through the Straits of Belle Isle."*
Boulder Clay the Product of Land-ice, — There is still
» "Memoirs of Boston Society of Natural History," voL L (1867), p. 228.


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another point connected with icebergs to which we must
allude, viz., the opinion that great masses of the boulder
clay of the glacial epoch were formed from the droppings
of icebergs. If boulder clay is at present being accumu-
lated in this manner, then traces of the boulder clay deposits
of former epochs might be expected to occur. It is perfectly
obvious that unstratified boulder clay could not have been
formed in this way. Stones, gravel, sand, clay, and mud, the
ingredients of boulder clay, tumbled all together fipom the back
of an iceberg, could not sink to the bottom of the sea without
separating. The stones would reach the bottom first, then, the
gravel, then the sand, then the clay, and last of all the mud,
and the whole would settle dowii in a stratified form. But,
besides, how cotdd the clay be derived from icebergs ? Ice-
bergs derive their materials from the land before they are
launched into the deep, and while they are in the form of land-
ice. The materials which are found on the backs of icebergs
are what fell upon the ice from mountain tops and crags pro-
jecting above the ice. Icebergs are chiefly derived fipom con-
tinental ice, such as that of Greenland, where the whole country
is buried under one continuous mass, with only a lofty moun-
tain peak here and there rising above the surface. And this is
no doubt the chief reason why so few icebergs have stones
upon their backs. The continental ice of Greenland is not,
like the glaciers of the Alps, covered with loose stones.
Dr. Robert Brown informs me that no moraine matter has
ever been seen on the inland ice of Greenland. It is per-
fectly plain that clay does not fall upon the ice. What falls
upon the ice is stones, blocks of rocks, and the loose dibris.
Clay and mud we know, from the accounts given by arctic
voyagers, are sometimes washed down upon the coast-ice ; but
certainly very little of either can possibly get upon an iceberg.
Arctic voyagers sometimes speak of seeing clay and mud upon
bergs ; but it is probable that if they had been near enough
they woidd have found that what they took for clay and mud
were merely dust and rubbish.


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Undoubtedly the boulder clay of many places bears unmis-
takable evidence of having been formed under water ; but it
does not on that account follow that it was formed from the
droppings of icebergs. The fact that the boulder clay in every
case is chiefly composed of materials derived from the country on
which the clay lies, proves that it was not formed from matter
transported by icebergs. The clay, no doubt, contains stones
and boidders belonging to other countries, which in some cases
may have been transported by icebergs ; but the clay itself has
not come from another country. But if the clay itself has been
derived from the country on which it lies, then it is absurd to
suppose that it was deposited from icebergs. The clay and
materials which are found on icebergs are derived from the
land on which the iceberg is formed ; but to suppose that ice-
bergs, after floating about upon the ocean, should always return
to the country which gave them birth, and there deposit their
loads, is rather an extravagant supposition.

From the facts and considerations adduced we are, I would
venture to presume, warranted to conclude that, with the
exception of what may have been produced by land-ice, very
little in the shape of boulder day or striated rocks belonging
to the glacial epoch lies buried under the ocean — and that when
the now existing land-surfaces are aU denuded, probably scarcely
a trace of the glacial epoch will then be found, except the huge
blocks that were transported by icebergs and dropped into the
sea. It is therefore probable that we have as much evidence of
the existence of a glacial epoch during former periods as the
geologists of future ages will have of the existence of a glacial
epoch during the Post-tertiary period, and that consequently
we are not warranted in concluding that the glacial epoch was
something imique in the geological history of our globe.

Palceontological Evidence. — ^It might be thought that if glacial
epochs have been numerous, we ought to have abundance of
palaK)ntological evidence of their existence. I do not know
if this necessarily follows. Let us take the glacial epoch itself
for example, which is quite a modem affair. Here we do not


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require to go and Bearch in the bottom of the sea for the
evidence of its existence ; for we have the sur&ce of the land
in almost identically the same state in which it was when the
ice left it, with the boidder clay and all the wreck of the ice
lying upon it. But what geologist, with all these materials before
him, would be able to find out from palseontological evidence
alone that there had been such an epoch P He might search
the whole, but would not be able to find fossil evidence from
which he could warrantably infer that the country had ever
been covered with ice. We have evidence in the fossils of the
Crag and other deposits of the existence of a colder condition
of climate prior to the true glacial period, and in the shell-beds
of the Clyde and other places of a similar state of matters after
the great ice-sheets had vanished away. But in regard to the
period of the true boulder clay or till, when the country was
enveloped in ice, palaeontology has almost nothing whatever to
tell us. "Whatever may be the cause," says Sir Charles
Lyell, " the fact is certain that over large areas in Scotland,
Ireland, and Wales, I might add throughout the northern
hemisphere on both sides of the Atlantic, the stratified
drift of the glacial period is very commonly devoid of

In the " flysch " of the Eocene of the Alps, to which we shall
have occasion to refer in the next chapter, in which the huge
blocks are found which prove the existence of ice-action during

Online LibraryJames CrollClimate and time in their geological relations: a theory of secular changes ... → online text (page 26 of 54)