In the region occupied by these erratic blocks, ridges of them and other detrital matter have been observed to run in lines, often for considerable distances. These are commonly known as skars, or ösars.* Count Rasoumouski would appear (in 1819) to have been among the first to remark upon those in Russia and Germany, observing that they usually occurred in lines having a direction from N.E. to S.W. M. Brongniart pointed out (in 1828), that those of Sweden, though sometimes inosculating, took a general direction from north to south.† Much discussion has arisen respecting the origin of these lines of accumulation. Upon the supposition that lines of blocks may have been accumulated by glaciers, and the drift of iceberg and coast ice in particular directions, and that upon the uprise of such lines of deposits, breaker action had been brought to bear upon them for a time, we should expect very complicated evidence.

as

In Northern America erratic blocks are found to occupy a large area, some being strewed as far south as 40° N. latitude. Here, in Northern Europe, the general drift of detritus appears to be from the northward to the southward, and blocks perched at various altitudes, scored and scratched surfaces of subjacent rocks, and ösars or lines of accumulation ‡ occur in the same manner. Such similar effects point to similar causes, and hence the explanations

from the coast of Kemi into the Bay of Onega, and from Russian Lapland into the Icy Sea, that is, in northerly, north-westerly, and north-easterly directions, as quoted also in the "Geology of Russia," vol. i., p. 528.

*It is worthy of remark that similar accumulations of this date, in Ireland, are known as Escars.

"Annales des Sciences Naturelles," 1828. M. d'Archiac observes (" Histoire des Progrès de la Géologie," 1848, tom. ii., p. 36,) that "the form of the ösars, their disposition, and their parallelism with the furrows and scratches of erosion, naturally lead to the idea of a current which has swept the southern part of Sweden from N.N.E. to S.S.W. M. Durocher has found, with M. Sefström, that the ösars were heaped up on the southern side of the mountains which, in that direction, opposed their course. The ösars in Finland, though less marked, have a direction from N. 25° W. to S. 25° E., one which, with the preceding, represents the radii of the semicircle in which the great erratic block deposit of Central Europe occurs "

In the "Geology of Russia in Europe and the Ural Mountains" will be found the views of its authors respecting skärs or ösars. A figure is given of an iceberg aground, and the consequences of its melting stated, lines of angular and rounded blocks being strewed, as the ice dissolved, by a current acting constantly in one direction.

An interesting account of two remarkable trains of angular erratic blocks in Berkshire, Massachusetts, is given by Professors Henry and William Rogers, in the "Boston Journal of Natural History," June, 1846. These two trains, one extending for 20 miles, both previously noticed by Dr. Reid and Professor Hitchcock, were traced to their sources. The blocks are generally large, the smaller being several feet in diameter. One weighs about 2,000 tons. The blocks gradually decrease in size to the S.E., those which have travelled farthest being the most worn. They are stated not to mingle with the general drift beneath them, the boulders and pebbles in which bear "the traces of a long-continued and violent rubbing." "Other long and narrow lines of huge erratic fragments are seen elsewhere in Berkshire, and abound,

offered have been of a similar general character.* A large amount of information has also been collected respecting the occurrence of these blocks, and of the polishing and scoring of subjacent rocks.† It is stated that the divergence of any blocks, such, for example, as those of the Alps, is not observed in the United States. Professor Henry Rogers points out that the scorings do not radiate from the high grounds; but that, amid the mountains of New England and in the great plains of the west, and in Pennsylvania, Vermont, and Massachusetts, they preserve a south-east direction at all their elevations; the lower parts of the great valleys being alone excepted. In the mountainous portions of the region, the heights and flanks exposed to the north and north-west are the most polished and scored. Blocks of large size have been found in New England, New York, and Pennsylvania, from 1,000 to 1,500 feet above the sea.

Erratic blocks are also found in South America. Mr. Darwin discovered them up the Santa Cruz river, Patagonia, in about 50° 10' S. latitude, and at about 67 miles from the nearest Cordillera. Nearer the mountains (at 55 miles) they became "extraordinarily numerous." One square block of chloritic schist measured 5 yards on each side, and projected 5 feet above the ground; another, more rounded, measured 60 feet in circumference. There were innumerable other fragments from 2 to 4 feet square." The great plain on which they stood was 1,400 feet above the sea, sloping gradually to sea cliffs of about 800 feet in height. Other boulders were found upon a plain, above another, elevated 440 feet, through

66

we think, in nearly all the mountainous districts of New England. One such train, originating apparently in the Lennox ridge, about two miles on the south of Pittsfield, crosses the Housatonic Valley, south-easterly, as far at least as the foot of the broad chain of hills in Washington. Some very extensive ones are to be seen on the western side of the White Mountains.

* These will be found in the works and memoirs of Hitchcock, Mather, Emmons, Hall, Rogers, Hubbart, Redfield, Jackson, Christy, Ch. Martins, and other geologists. We are indebted to Dr. Bigsby for an early notice of the erratic blocks of North America. (Trans. Geol. Soc., London, vol. i., second series.)

In 1833, Professor Hitchcock ("Report on the Geology of Massachusetts," art. Diluvium,) adduced abundant evidence of the northern origin of these blocks in the districts described by him. The like was also done at an early date for other portions of North America, by Messrs. Lapham, Jackson, Alger, and others. The observer will find an able summary of the facts known in 1846, on this subject, in Professor Hitchcock's Address to a meeting of the Association of American Geologists in that year. Professor Henry Rogers also treated in a general manner of the American erratic blocks in his Address to the same scientific body in 1844, (American Journal of Science, vol. xlvii.) Another general summary, up to 1848, is given by the Vicomte d'Archiac, ("Histoire des Progrès de la Géologie," tom. ii., chap. 9, Terrain Quaternaire de l'Amérique du Nord).

Darwin, "On the Distribution of Erratic Boulders, and on the Contemporaneous Unstratified Deposits of South America."-Geol. Trans., second series, vol. vi. p. 415.

which the same river flows, and at 800 feet above the sea. In the valley of the Santa Cruz, and at 30 or 40 miles from the Cordillera, (the highest parts in this latitude rise to about 6,400 feet,) blocks of granite, syenite, and conglomerate, not found in the more elevated plains, were detected. Mr. Darwin infers that these are not the wreck of those observed on the higher plain, but that they have been subsequently transported from the Cordillera. He had not opportunities of observing other erratic blocks in Patagonia, but refers to the great fragments of rocks noticed by Captain King on the surface of Cape Gregory, a headland, about 800 feet high, on the northern shore of the Strait of Magellan. Mr. Darwin also describes rock fragments of various dimensions and kinds in Tierra del Fuego and the Strait of Magellan, amid stratified and unstratified accumulations of a similar general character to those of this geological date in Europe.* Many of the erratic blocks are large, one at St. Sebastian's Bay, east coast of Tierra del Fuego, was 47 feet in circumference, and projected 5 feet from the sand beach. The general drift of these deposits is considered to be from the westward, the manner in which the transported fragments of rock would be carried by a current similar to that which sweeps against the present land. On the north of Cape Virgins, close outside the Strait of Magellan, the imbedded fragments are considered to have been transported 120 geographical miles or more from the west and south-west. On the northern and eastern coasts of the Island of Chiloe, extending from 43° 26', to 41° 46′ S. latitude, Mr. Darwin detected an abundance of granite and syenite boulders, from the beach to a height of 200 feet on the land. He infers that these boulders have travelled more than 40 miles from the Cordillera on the east.†

fine-grained, earthy or

At Elizabeth Island, Strait of Magellan, there occurs, argillaceous sandstone, in very thin, horizontal, and sometimes inclined laminæ, and often associated with curved layers of gravel. On the borders, however, of the eastward part of the Strait of Magellan, this fine-grained formation often passes into, and alternates with, great unstratified beds, either of an earthy consistence and whitish colour, or of a dark colour and of a consistence like hardened coarse-grained mud, with the particles not separated according to their size. These beds contain angular and rounded fragments of various kinds of rock, together with great boulders."— Geol. Trans., second series, vol. vi., p. 418. Variations of these accumulations are noticed as occurring in other places, and two sections of contorted and confused beds at Gregory Bay are given, and Mr. Darwin infers that this disturbance may have been produced by grounded icebergs.

"The larger boulders were quite angular." . . . "One mass of granite at Chacao was a rectangular oblong, measuring 15 feet by 11 feet, and 9 feet high. Another, on the north shore of Lemuy islet, was pentagonal, quite angular, and 11 feet on each side; it projected about 12 feet above the sand, with one point 16 feet high: this fragment of rock almost equals the larger blocks on the Jura."- Geol. Trans., second series, vol. vi., p. 425.

CHAPTER XV.

MOLLUSC REMAINS IN SUPERFICIAL DETRITUS.-ARCTIC SHELLS FOUND IN BRITISH DEPOSITS.—EVIDENCE OF A COLDER CLIMATE IN BRITAIN.— EXTINCT SIBERIAN ELEPHANT.-CHANGES OF LAND AND SEA IN NORTHERN EUROPE.-EXTINCTION OF THE GREAT NORTHERN MAMMALS.-RANGE OF THE MAMMOTH.-FROZEN SOIL OF SIBERIA.

UPON the supposition of the submergence of a large portion of the present dry land of Northern Europe, Asia, and America, beneath seas upon which ice was formed, and into which glaciers protruded in lower latitudes than at present, we should expect to discover in the marine deposits of these regions, and of the period now upraised into the atmosphere, evidences of the marine animal life of the time having corresponded with the low temperature to which it was then exposed. This evidence is considered to have been found.

As regards the British Islands, Mr. Trimmer pointed out, in 1831, that amid the detrital accumulation referred to this date, and at a considerable height above the sea (since ascertained to be 1,392 feet), upon Moel Trefan (one of the hills on the outskirts of the chief Caernarvonshire mountains), fragments of Buccinum, Venus, Natica, and Turbo of existing species were found. He also stated that on the flanks of the Snowdonian mountains, and between them and the adjoining sea, in the Menai Straits, there were large accumulations of boulders and fragments derived from a distance, (among them chalk flints,) mingled with others of a local kind. Mr. Trimmer subsequently (1838) published a more general statement on the same subject, noticing various localities where he and others had found shells, of a similar character, in deposits referred to this date.*

The first communication was made to the Geological Society of London (Proceedings of that Society, vol. i.); the second to the Geological Society of Dublin, in a memoir, in two parts, entitled, "On the Diluvial or Northern Drift on the Eastern

Commenting on the facts observed by Mr. Trimmer on Moel Trefan, Sir Roderick Murchison (in 1832) inferred from the previous discovery of shells of existing species in the Lancashire gravels and sands by Mr. Gilbertson, one which he was enabled to confirm from actual observation, and from finding similar accumulations over a large tract of country, that the materials of the ancient shore of Lancashire and of the estuary of the Ribble, were deposited during a long protracted period, and "were elevated and laid dry after the creation of many of the existing species of molluscs."* Numerous facts of the like kind were noticed by different observers ;† but the inference as to a temperature less at that geological time than at present, as shown by the remains of molluscs, does not appear to have taken a distinct form until Mr. Smith, of Jordan Hill, published his views on the subject in 1839. He discovered shells in places where their animals had lived and died, in the counties of Lanark, Renfrew, and Dumbarton, and hence inferred their entombment by depression, a half-tide deposit being converted into one in a deeper sea. From these and other researches, Mr. Smith obtained a mass of evidence which led him to conclude, from the remains of the molluscs discovered in deposits of this date in different localities, that the climate of the British Islands had then been colder than it now is, more especially as Arctic molluscs, not

and Western side of the Cambrian Chain, and its Connexion with a similar Deposit on the Eastern side of Ireland, at Bray, Howth, and Glenismaule."-(Journal of the Geological Society of Dublin.) Mr. Trimmer mentions that, prior to his discovery of the shells on Moel Trefan, Mr. Gilbertson had found shells of existing species in gravel and sand near Preston, Lancashire, and that Mr. Underwood had observed furrows and scratches on the surface of rocks laid bare among the Snowdonian mountains, when the great road from Bangor to Shrewsbury was in progress.

* Address, as President, to the Geological Society of London, February, 1832.— Proceedings of that Society, vol. i, p. 366.

Among the observations of the time, and as important for the locality noticed, should be mentioned those of Sir Philip Egerton, "On a Bed of Gravel containing Marine Shells, of recent Species, at Wellington, Cheshire" (Proceedings of the Geological Society, vol. ii., p. 189, April 1835). Sir Philip notices the remains of Turritella terebra, Cardium edule, and Murex arenaceus, and infers that there had been an alteration of 70 feet in the level of land and sea, as regards the locality, since the deposit was formed. In 1837, Mr. Strickland ("On the Nature and Origin of the various kinds of transported Gravel occurring in England," read at the British Association in that year) took a general view of the stratified and unstratified character of these deposits, and divided them into-1. Marine drift, formed when the central portions of England were under the sea; and, 2. Fluviatile drift, when they were above its level, forming dry land, the first composed of (a) erratic gravel, without chalk flints; (b) erratic gravel, with chalk flints; and (c) local, or nonerratic gravel.

"On the late Changes of the relative Levels of the Land and Sea in the British Islands" (Memoirs of the Wernerian Natural History Society, Edinburgh, vol. viii., p. 49, &c.) In this memoir Mr. Smith most carefully cites all those who had previously discovered facts relating to the subject, giving an account of these facts.