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58 IMPACTED BOULDERS.
forces in operation above water as compared with these ice-masses, so long as
they continue afloat, than the majestic immobility of the berg seen on the
11th of October during the continuance of one of the severest gales we have
encountered in these waters.
In illustration of the enormous force requisite to move a mass of pack-ice even
of moderate dimensions, I would mention that on one occasion, in the vicinity of
Frederickshaab, the port paddle came into collision with a piece the superficial
diameter of which was about 70 or 80 feet, whilst its average height above water
was about 3^ feet, and that, instead of the ship causing the mass of ice to
oscillate, the paddle actually mounted on the ice-surface, and caused the ship
to heel over until it again became disengaged.
The soUtary instance in which I observed evidence of large masses of rock or
boulder having been impacted in a berg also occurred during one of our attempts
to approach Frederickshaab. This berg was probably about 120 feet in height,
and from 300 to 400 feet in length. About 20 feet above the water-line two
large cavern-like apertures existed, the inner surfaces of which retained the mud
and detritus left behind on the disengagement of the boulders that originally
occupied them. Several small stones still remained imbedded; and around them
were to be seen smaller cavities, precisely resembling the two first described.
Indeed, I should never have suspected that boulders had lodged in the larger
cavities, but for the similarity in character between them and the smaller empty
ones. I infer that the larger could not have materially increased in diameter by
the process of thawing or wave-washing, solely from the presence of the detritus,
which in that case would have disappeared.
At Goodhaab I repeatedly came across small bergs in the fiords, laden with
mud and detritus, and sometimes carrying imbedded stones of moderate size.
One of these I was induced to examine more closely than perhaps I should
otherwise have done, having “ stalked ” what I conceived to be a large black
bird perched halfway up on its face, and on close approach discovered it to be
one of these impacted boulders, about a foot in diameter.
The large shoal called the “ Tallert Bank,” to which I have drawn attention in
a former page as being composed of detritus brought down from the interior of
the land by a river debouching under the great ice-blink, affords an example of
the conditions under which the smaller class of bergs receive detritus. That
SUBGLACIAL VALLEYS. 59
bank, which is a drift-bed now in process of formation, would in all probability
present every condition, both as regards mineralogical composition and
the character of its organic remains, that occurs in the ancient drift-beds of the
Post-pliocene period.
Whilst at Julianshaab, I was informed by Mr. Hoyer, the Assistant Superintendent
of the colony, who has explored the so-called continental ice of South
Greenland for a considerable distance into the interior, that crevasses are occasionally
to be met with, of no great width, but whose depth is so great that a
fragment of ice dropped into them can be heard to reach the bottom after
the lapse of a very considerable interval ; whilst in some places the sound of
running water and cascades at great depths can be distinctly recognized. The
Esquimaux assert that, during the most severe period of the winter, the reindeer
flock together in herds under the hollow portions of the continental ice, and that
they actually find food, such as lichens, in these vast ice-vaulted wildernesses
when none is attainable elsewhere. Without pretending to deal with the proofs
that are required before such a statement can be accepted as a fact, I must say
I am unable to adduce any weighty reasons why it should not be so ; whilst, on
the other hand, sundry plausible arguments could be brought forward which
tend to show not only that such sub-glacial tracts may, but in all probability do
exist.
In the event of a glacier forming in a valley traversed by a shallow stream
during the warmer months, the first effect of the influx of a much augmented
volume of water at a temperature considerably above freezing-point would be to
produce a series of arched passages, which would subsequently increase in vertical
dimensions in consequence of the obstructed outflow keeping them filled, and
thus subject to a protracted thawing action. On the recurrence of winter, the
onward progress of the glacier would more or less completely block up the outlet,
without obUterating the previously formed subglacial channel. On the
return of summer, the now enlarged channel would at once be filled up with
water of sufficiently high temperature to extend its boundary walls still fui'ther,
—these two operations being repeated indefinitely through a lapse of centuries,
and eventually resulting in the subglacial tract referred to. Under the same
circumstances the waters flowing down into this tract would convey and deposit
the spores of lichens, and possibly the seeds of phanerogamic plants, which, on
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