The Antiquity of Man Part 32

These cliffs extend through the north-eastern coast of the island, called Moens Klint,* where the Chalk precipices are bold and picturesque, being 300 and 400 feet high, with tall beech-trees growing on their summits, and covered here and there at their base with huge taluses of fallen drift, verdant with wild shrubs and gra.s.s, by which the monotony of a continuous range of white Chalk cliffs is prevented.

(* Puggaard, "Geologie d. Insel Moen" Bern 1851; and "Bulletin de la Societe Geologique de France" 1851.)

[Ill.u.s.tration: Figure 47 and 48. Southern Extremity Of Moens Klint]

(FIGURE 47. SOUTHERN EXTREMITY OF MOENS KLINT (PUGGAARD).

A. Horizontal drift.

B. Chalk and overlying drift beginning to rise.

C. First flexure and fault. Height of cliff at this point, 180 feet.)

(FIGURE 48. SECTION OF MOENS KLINT (PUGGAARD), CONTINUED FROM FIGURE 47.

S. Fossil sh.e.l.ls of recent species in the drift at this point.

G. Greatest height near G, 280 feet.)

In the low part of the island, at A, Figure 47, or the southern extremity of the line of section above alluded to, the drift is horizontal, but when we reach B, a change, both in the height of the cliffs and in the inclination of the strata, begins to be perceptible, and the Chalk Number 1 soon makes its appearance from beneath the overlying members of the drift Numbers 2, 3, 4, and 5.

This Chalk, with its layers of flints, is so like that of England as to require no description. The inc.u.mbent drift consists of the following subdivisions, beginning with the lowest:

Number 2. Stratified loam and sand, 5 feet thick, containing at one spot near the base of the cliff, at s, Figure 48, Cardium edule, Tellina solidula, and Turritella, with fragments of other sh.e.l.ls. Between Number 2 and the Chalk Number 1, there usually intervenes a breccia of broken flints.

Number 3. Unstratified blue clay or till, with small pebbles and fragments of Scandinavian rocks occasionally scattered through it, 20 feet thick.

Number 4. A second unstratified ma.s.s of yellow and more sandy clay 40 feet thick, with pebbles and angular polished and striated blocks of granite and other Scandinavian rocks, transported from a distance.

Number 5. Stratified sands and gravel, with occasionally large erratic blocks; the whole ma.s.s varying from 40 to 100 feet in thickness, but this only in a few spots.

The angularity of many of the blocks in Numbers 3 and 4, the glaciated surfaces of others, and the transportation from a distance attested by their crystalline nature, prove them to belong to the northern drift or glacial period.

It will be seen that the four subdivisions 2, 3, 4, and 5 begin to rise at B, Figure 47, and that at C, where the cliff is 180 feet high, there is a sharp flexure shared equally by the Chalk and the inc.u.mbent drift.

Between D and G, Figure 48, we observe a great fracture in the rocks with synclinal and anticlinal folds, exhibited in cliffs nearly 300 feet high, the drift beds partic.i.p.ating in all the bendings of the Chalk; that is to say, the three lower members of the drift, including Number 2, which, at the point S in this diagram, contains the sh.e.l.ls of Recent species before alluded to.

Near the northern end of the Moens Klint, at a place called "Taler,"

more than 300 feet high, are seen similar folds, so sharp that there is an appearance of four distinct alternations of the glacial and Cretaceous formations in vertical or highly inclined beds; the Chalk at one point bending over so that the position of all the beds is reversed.

[Ill.u.s.tration: Figure 49. Post-Glacial Disturbances]

(FIGURE 49. POST-GLACIAL DISTURBANCES OF VERTICAL, FOLDED, AND s.h.i.+FTED STRATA OF CHALK AND DRIFT, IN THE DRONNINGESTOL, MOEN, HEIGHT 400 FEET (PUGGAARD).

1. Chalk with flints.

2. Marine stratified loam, lowest member of glacial formation.

3. Blue clay or till, with erratic blocks unstratified.

4. Yellow sandy till, with pebbles and glaciated boulders.

5. Stratified sand and gravel with erratics.)

But the most wonderful s.h.i.+ftings and faultings of the beds are observable in the Dronningestol part of the same cliff, 400 feet in perpendicular height, where, as shown in Figure 49, the drift is thoroughly entangled and mixed up with the dislocated Chalk.

If we follow the lines of fault, we may see, says M. Puggaard, along the planes of contact of the s.h.i.+fted beds, the marks of polis.h.i.+ng and rubbing which the Chalk flints have undergone, as have many stones in the gravel of the drift, and some of these have also been forced into the soft Chalk. The manner in which the top of some of the arches of bent Chalk have been cut off in this and several adjoining sections, attests the great denudation which accompanied the disturbances, portions of the bent strata having been removed, probably while they were emerging from beneath the sea.

M. Puggaard has deduced the following conclusions from his study of these cliffs.

First. The white Chalk, when it was still in horizontal stratification, but after it had suffered considerable denudation, subsided gradually, so that the lower beds of drift Number 2, with their littoral sh.e.l.ls, were superimposed on the Chalk in a shallow sea.

Second. The overlying unstratified boulder clays 3 and 4 were thrown down in deeper water by the aid of floating ice coming from the north.

Third. Irregular subsidences then began, and occasionally partial failures of support, causing the bending and sometimes the engulfment of overlying ma.s.ses both of the Chalk and drift, and causing the various dislocations above described and depicted. The downward movement continued till it exceeded 400 feet, for upon the surface even of Number 5, in some parts of the island, lie huge erratics 20 feet or more in diameter, which imply that they were carried by ice in a sea of sufficient depth to float large icebergs. 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.

Fourth. 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 Moen, 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 east-south-east to west-north-west, with lines of fracture at right angles to them; the second running from south-south-east to north-north-west, also with fractures in a transverse direction; and lastly, a sinking in a north and south direction, with other subsidences of contemporaneous date running at right angles or east and west.

When we approach the north-west end of Moens 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 Moens 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 Moen 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 have been missing, where there has been so much denudation, 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 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. Horbye on the mountains of the Dovrefjeld in lat.i.tude 62 degrees north, where the striation and friction is said to be independent of the present shape and slope of the mountains.*

(* "Observations sur les Phenomenes d'Erosion en Norwege"

1857.)

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, Chapter 13), would not account for the deviation of the furrows and striae 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 sh.e.l.ls of Recent species to the height of several hundred feet, have been tolerably uniform over very wide s.p.a.ces; yet a remarkable exception to this rule was observed by M. Bravais at Altenfjord in Finmark, between lat.i.tude 70 and 71 degrees north. 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 30 miles from south to north along the borders of a fjord rising gradually from a height of 85 feet to an elevation of 220 feet above the sea, or at the rate of about 4 feet in a mile.*

(* "Proceedings of the Geological Society" 1845 volume 4 page 94.)

To pa.s.s 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 sh.o.r.es of Cook's Straits, which at one point, called Muko-muka, was so unequal as to amount to 9 feet vertically, while it declined gradually from this maximum of upheaval in a distance of about 23 miles north-west 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 shock in executing public works on the coast, ascertained that the extreme upheaval of certain ancient rocks followed a line of fault running at least 90 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 Palaeozoic rocks.*

(* "Bulletin de la Societe Geologique de France" volume 13 1856 page 660, where I have described the facts communicated to me by Messrs. Roberts and Walter Mantell.)

The repet.i.tion 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 compa.s.s 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 Moen, for the princ.i.p.al movements in any given period seem to be of a more uniform kind, by which the topography of limited districts and the position of the strata are not visibly altered except in their height relatively 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 acc.u.mulation. 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 Palaeozoic 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 Moen 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 Number 5, Figure 49, with its large erratic blocks, were deposited, as some of those beds occurring in the disturbed parts of Moen appear to have escaped the convulsions to which Numbers 2, 3, and 4 were subjected. If this be so, the whole derangement, although Pleistocene, 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.

CHAPTER 18. -- THE GLACIAL PERIOD IN NORTH AMERICA.

Post-glacial Strata containing Remains of Mastodon giganteus in North America.

Scarcity of Marine Sh.e.l.ls 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 Berks.h.i.+re, Ma.s.sachusetts.

Description of their Linear Arrangement and Points of Departure.

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.