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CHAP. XVII.

DIRECTIONS OF SUCCESSIVE MOVEMENTS.

34,

of sufficient depth to float large ice-bergs. But these big erratics, says Puggaard, never enter into the fissures as they would have done had they been of date anterior to the convulsions.

4th. After this subsidence, the re-elevation and partial denudation of the cretaceous and glacial beds took place during a general upward movement, like that now experienced in parts of Sweden and Norway.

In regard to the lines of movement in Möen, M. Puggaard believes, after an elaborate comparison of the cliffs with the interior of the island, that they took at least three distinct directions at as many successive eras, all of post-glacial date; the first line running from ESE. to WNW., with lines of fracture at right angles to them; the second running from SSE. to NNW., also with fractures in a transverse direction; and lastly, a sinking in a N. and S. direction, with other subsidences of contemporaneous date running at right angles, or E. and W.

When we approach the north-west end of Möens Klint, or the range of coast above described, the strata begin to be less bent and broken, and, after travelling for a short distance beyond, we find the chalk and overlying drift in the same horizontal position as at the southern end of the Möens Klint. What makes these convulsions the more striking is the fact that in the other adjoining Danish islands, as well as in a large part of Möen itself, both the secondary and tertiary formations are quite undisturbed.

It is impossible to behold such effects of reiterated local movements, all of post-tertiary date, without reflecting that, but for the accidental presence of the stratified drift, all of which might easily, where there has been so much denudation, have been missing, even if it had once existed, we might have referred the verticality and flexures and faults of the rocks to an ancient period, such as the era between the chalk

with flints and the Maestricht chalk, or to the time of the latter formation, or to the eocene, or miocene, or older pliocene eras, even the last of them, long prior to the commencement of the glacial epoch. Hence we may be permitted to suspect that in some other regions, where we have no such means at our command for testing the exact date of certain movements, the time of their occurrence may be far more modern than we usually suppose. In this way some apparent anomalies in the position of erratic blocks, seen occasionally at great heights above the parent rocks from which they have been detached, might be explained, as well as the irregular direction of certain glacial furrows like those described by Professor Keilhau and Mr. Hörbye on the mountains of the Dovrefjeld in lat. 62° N., where the striation and friction is said to be independent of the present shape and slope of the mountains.* Although even in such cases it remains to be proved whether a general crust of continental ice, like that of Greenland, described by Rink (see above, p. 235), would not account for the deviation of the furrows and striæ from the normal directions which they ought to have followed had they been due to separate glaciers filling the existing valleys.

It appears that in general the upward movements in Scandinavia, which have raised sea-beaches containing marine shells of recent species to the height of several hundred feet, have been tolerably uniform over very wide spaces; yet a remarkable exception to this rule was observed by M. Bravais, at Altenfiord, in Finmark, between lat. 70° and 71° N. An ancient water-level, indicated by a sandy deposit forming a terrace, and by marks of the erosion of the waves, can be followed for thirty miles from south to north along the borders of a fiord rising gradually from a height of eighty-five feet to an elevation of 220 feet above the sea, or at the rate of about four feet in a mile.t

* Observations sur les Phénomènes d'Érosion en Norwege, 1857.

† Proceedings of the Geological Society, 1845, vol. iv. p. 94.

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To pass to another and very remote part of the world, we have witnessed, so late as January 1855, in the northern island of New Zealand, a sudden and permanent rise of land on the northern shores of Cook's straits, which at one point, called Muko-muka, was so unequal as to amount to nine feet vertically, while it declined gradually from this maximum of upheaval in a distance of about twenty-three miles northwest of the greatest rise, to a point where no change of level was perceptible. Mr. Edward Roberts, of the Royal Engineers, employed by the British Government at the time of the shoek in executing public works on the coast, ascertained that the extreme upheaval of certain ancient rocks followed a line of fault running at least ninety miles from south to north into the interior; and, what is of great geological interest, immediately to the east of this fault, the country, consisting of tertiary strata, remained unmoved or stationary; a fact well established by the position of a line of nullipores marking the sea-level before the earthquake, both on the surface of the tertiary and paleozoic rocks.*

The repetition of such unequal movements, especially if they recurred at intervals along the same lines of fracture, would in the course of ages cause the strata to dip at a high angle in one direction, while towards the opposite point of the compass they would terminate abruptly in a steep escarpment.

But it is probable that the multiplication of such movements in the post-tertiary period has rarely been so great as to produce results like those above described in Möen, for the principal movements in any given period seem to be of that more uniform kind spoken of at p. 334, by which the topography of limited districts and the position of the strata are not visibly altered except in their height relatively

* Bulletin de la Société Géologique de France, vol xiii. p. 660, 1856, where I have described the facts com

municated to me by Messrs. Roberts and Walter Mantell.

to the sea. Were it otherwise we should not find conformable strata of all ages, including the primary fossiliferous of shallow-water origin, which must have remained horizontal throughout vast areas during downward movements of several thousand feet, going on at the period of their accumulation. Still less should we find the same primary strata, such as the carboniferous, Devonian, or Silurian, still remaining horizontal over thousands of square leagues, as in parts of North America and Russia, having escaped dislocation and flexure throughout the entire series of epochs which separate paleozoie from recent times. Not that they have been motionless, for they have undergone so much denudation, and of such a kind, as can only be explained by supposing the strata to have been subjected to great oscillations of level, and exposed in some cases repeatedly to the destroying and planing action of the waves of the sea.

It seems probable that the successive convulsions in Möen were contemporary with those upward and downward movements of the glacial period which were described in the thirteenth and some of the following chapters, and that they ended before the upper beds of No. 5, p. 346, with its large erratic blocks, were deposited, as some of those beds occurring in the disturbed parts of Möen appear to have escaped the convulsions to which Nos. 2, 3, and 4 were subjected. If this be so, the whole derangement, although post-pliocene, may have been anterior to the human epoch, or rather to the earliest date to which the existence of man has as yet been traced back.

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POST-GLACIAL STRATA CONTAINING REMAINS OF MASTODON GIGANTEUS
IN NORTH AMERICA - SCARCITY OF MARINE SHELLS IN GLACIAL DRIFT
OF CANADA AND THE UNITED STATES — GREATER SOUTHERN EXTENSION
OF ICE-ACTION IN NORTH AMERICA THAN IN EUROPE — TRAINS OF
ERRATIC BLOCKS OF VAST SIZE IN BERKSHIRE, MASSACHUSETTS —
DESCRIPTION OF THEIR LINEAR ARRANGEMENT AND POINTS OF DE-
PARTURE — THEIR TRANSPORTATION REFERRED TO FLOATING AND
COAST ICE-GENERAL REMARKS ON THE CAUSES OF FORMER CHANGES
OF CLIMATE AT SUCCESSIVE GEOLOGICAL EPOCHS SUPPOSED EFFECTS
OF THE DIVERSION OF THE GULF STREAM IN A NORTHERLY INSTEAD
OF NORTH-EASTERLY DIRECTION — DEVELOPMENT OF EXTREME COLD
ON THE OPPOSITE SIDES OF THE ATLANTIC IN THE GLACIAL PERIOD
NOT STRICTLY SIMULTANEOUS - NUMBER OF SPECIES OF PLANTS AND
ANIMALS COMMON TO PRE-GLACIAL AND POST-GLACIAL TIMES.

An the North American Continent, between the arctic U circle and the 42nd parallel of latitude, we meet with signs of ice-action on a scale as grand if not grander than in Europe; and there also the excess of cold appears to have been first felt, at the close of the tertiary, and to have continued throughout a large portion of the post-pliocene period.

The general absence of organic remains in the North American glacial formation, makes it as difficult as in Europe, to determine what mammalia lived on the continent at the time of the most intense refrigeration, or when extensive areas were becoming strewed over with glacial drift and erratic blocks, but it is certain that a large proboscidean now extinct, the Mastodon giganteus Cuv., together with many other quadrupeds, some of them now living and others extinct, played a conspicuous part in the post-glacial era. By its frequency as a fossil species, this pachyderm represents

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