blocks of granite, from 15 to 25 feet in diameter, on the Côteau des Prairies, to the west of Lake Superior, several hundred miles from the nearest rock of that kind in place, which lies northward.

3. Mr. Darwin affirms, that in the intertropical parts of America, Africa, and Asia, erratic blocks have never been observed, nor at the Cape of Good Hope, nor in Australia. Though this complete limitation of them to the colder regions of the globe may be deemed an unsettled point, it is certain that such phenomena are far less frequent and extensive in equatorial countries. Beyond 41° of south latitude in South America, the appearance of drift is common, upon the vast plains of Patagonia and Chili.

4. Rocks in situ, or in place, very frequently exhibit a marking with fine linear striæ or scratches, larger grooves, and even furrows, with a smooth and polished aspect of the surface, like that which the rapid passage of heavy masses over them would produce. Transatlantic facts of this description have been carefully collected by Professors Hitchcock and Rogers, from whom a few particulars may be introduced. In various parts of Massachusetts the striæ are very obvious and distinct, frequent on the hard sienitic rocks, though often these are merely smoothed, and sometimes polished. They are visible on the gneiss at the top of the Wachusett mountain, the highest in the eastern part of the state, 2000 feet above the ocean. The precipitous hills and the lower grounds of the Connecticut river valley are covered with them, their direction being north and south, inclining a few points east of south, and west of north. Mount Everett, 2600 feet above the sea level, has been worn over its whole surface, and the striæ are very visible in many places, though so long exposed naked to atmospheric and decomposing agencies. Mount Monadnoc, 3250 feet high, little else than a naked mass of mica-slate, of peculiar character, and almost destitute of stratification, has been from top to bottom scarified and scratched, the striæ running about north-west and south-east. Similar markings appear on the summits of all the Appallachian chain in Pennsylvania, which observe the same direction, and particularly, around the Wyoming valley the tops of the mountains are covered with parallel striæ. It is impossible, says one of the authorities named, to stand upon these lofty and precipitous ridges, and witness this phenomenon, without being struck with the great power and extent of the agency that has thus left its traces upon some of the most elevated spots in New England. The cut

In the annexed view, taken from a quarry of clay-slate in the state of Vermont, the perpendicular strata appear broken, and partially overturned, towards the summit.

The occurrence of drift, and of erratic blocks, constitutes one of the most complicated

and difficult problems of geology; nor has any theory yet been proposed offering a solution of it which is perfectly satisfactory. Some reasons have already been assigned for rejecting the long prevalent opinion that these phenomena resulted from the deluge

of Noah; namely, the presence of animals of extinct species, and some of extinct genera in the drift, with the absence of the remains of human beings, and of all vestiges of the arts and operations of man: and, in addition, it may be remarked, that if that event was local, confined to a part of southwestern Asia, as we have previously argued, it is further inadmissible as an explanation of effects certainly common to the whole northern hemisphere, and to the southern extremities of America. But the single consideration that the vast masses of gravel and blocks strewed over such extensive areas, do not belong to one violent and transitory period, but have been aggregated at different epochs, by causes sometimes operating feebly and slowly, and at other times violently and powerfully-the evidence of which is irresistible to those who have studied the subject-is amply sufficient by itself to disprove the idea of these accumulations being the consequence of the transient flood recorded in the sacred history.

It would require a volume to detail and discuss the various views of scientific inquirers respecting the drift deposits. An outline of the principal theories will suffice. 1. The sudden elevation of chains of mountains, while yet wholly or in part beneath the waters, which, rushing away from the axis of elevation, would transport detritus and blocks in various directions, has been suggested to account for the phenomena. The Alps have been referred to, as supplying some evidence in favour of this view. They appear to have been upheaved, if not from the ocean, yet to a considerable height, after the deposition of the tertiary strata, for patches of these strata are found capping their summits, and lying in their mountain valleys, while the drift is scattered in all directions from the central axis, on the Jura range, and on the plains of Lombardy. It is very likely that this has been influential in the production of drift; but though the paroxysmal elevation of a mountain chain from submergence would cause the waters to rush away violently from it, sweeping along a vast amount of detritus, yet a sudden and transient rush is inadequate to the effect, which in many instances evinces the action of a disturbing cause for a considerable length of time. 2. Strong currents, waves, and tides of the ocean, bearing icebergs upon their bosom, while the districts covered with far-borne detritus and blocks were beneath the sea, have been proposed to explain their accumulation upon them, the districts being subsequently elevated. This theory has evidence in its favour, for in a former section we have noticed the transporting power of icebergs with reference to the solid materials of the land; and it admits not of a doubt, that if the floor of the north Atlantic were now laid bare, we should see its surface covered with erratic blocks borne thither by the icy masses which annually melt away in its waters, derived from the shores of Greenland and Spitzbergen. But this can only be admitted as explaining part of the case, for it can scarcely apply to the drift containing the bones of the elephant and mastodon, with the other terrestrial quadrupeds. 3. It has been conceived that a powerful and extensive subaqueous elevation took place in the arctic regions, driving the northern ocean southward, over Great Britain, the north of Europe and America, bearing along masses of ice, blocks, and detritus; and that this vertical movement of the bed of the polar deep transpired repeatedly, producing

successive waves of translation, which invaded the existing dry land, destroyed its organic life, and spread over it the various boulders and foreign débris that now appear upon its surface. This hypothesis receives support from several considerations. It is in harmony with the positive events of bygone ages, and of the present epoch, as in the formation of new islands, and the tremendous wave that shattered the coast of Portugal during the earthquake of Lisbon. It is mathematically demonstrable that sudden vertical elevations, each not exceeding 58 feet in the case of an ocean of 300 or 400 feet in depth, would produce waves having the power of hurling on enormous blocks, sand, and gravel to vast distances, and over considerable inequalities, while it accounts for the southerly direction of the drift, and the frequent presence of sea-shells in the same sepulchre with the remains of land quadrupeds. 4. Agassiz, struck with the transporting force of glaciers, which advance by their own gravitation upon inclined surfaces, and break off masses of rock from the sides of the valleys, bearing them away to a distant locality in the course of years, has endeavoured to show that the drift around the flanks of the Alps has been abstracted from the mountains, and carried thither by ancient and more extensive glaciers, which once covered, in fact, the whole of Switzerland. Starting from this point, he has attempted to establish a general glacial theory, according to which a sudden reduction took place in the temperature of the surface of the globe, at the close of the tertiary period, whereby all organic life was destroyed, and the northern regions were converted into one vast mer de glace, which sent out enormous glaciers in a southerly direction. These he conceives to have smoothed, furrowed, and striated the rock-surfaces over which they passed, and to have carried along with them masses of entangled blocks and detritus, which were distributed far and wide, by the violent torrents occasioned through a raising of the temperature melting the glaciers. The development alone of this theory is due to Agassiz, for it was first suggested by M. Venetz, a Swiss engineer, and afterwards advocated by M. Charpentier. The reader will anticipate the chief difficulty in its way, the marked temporary alteration of the temperature, which could only have transpired through some transient derangement in the planetary relations of our globe. These are the chief theories proposed respecting the deposits under consideration, and probably a variety of agencies, to which each hypothesis contributes, has operated in their production.

CHAPTER XII.

ALLUVIUM.-RECENT FORMATIONS.

THE term diluvium, applied to the great collections of gravel and detached blocks, from the idea that they originated with the historic deluge, is still retained in such a connection, because those accumulations indicate the extraordinary action of water, either in the form of strong oceanic currents, while the localities were in a state of submergence, or of waves of translation overspreading the land, produced by submarine disturbance, or torrents proceeding from rapidly-melting glaciers. On the other hand, the term alluvium is used to denote those formations of the modern and current epoch which result from the ordinary action of water; and, etymologically, it can only be properly employed in relation to aqueous products. But its more comprehensive application is sanctioned by usage,

Cyclopean Remains, Mycene

and may be granted in this place as a matter of convenience. It occurs therefore at the head of this chapter as a general title for those superficial formations which appear to have transpired since our planet received its present configuration of land and sea, and Man became its occupant and master, which are now in course of production, whether due to aqueous, igneous, atmospheric, organic, or human agency, the effects of one or of several of these causes combined. In some of these recent aggregations we meet with the remains of man and contemporaneous animals and plants, with human utensils and ornaments also, characteristic of the ancient British age in our own country, the Etruscan in Italy, the Pelasgic in Greece, and the era of the Pharaohs along the banks of the Nile. But we discover no bones that can be specifically identified as those of the great quadrupeds of the drift, which probably mostly perished in those physical changes under which it accumulated, subsequent to which the present state of things commenced, and man, with the existing animal races, was created. Some have supposed, indeed, that America had its droves of mastodons and megatherida browsing upon its savannahs down to a comparatively modern period; and good evidence supports the idea, that the gigantic horned elk continued to be an inhabitant of Europe coexistent with the human race. Such conclusions, supposing them to be established, are in harmony with the views already expressed respecting the first appearance of the present animal races as produced around several centres of creation, not contemporaneously, our sacred history dealing merely with one of those districts, the most recent, that in which the primitive man was placed. There is no difficulty in conceiving of the extinction of some tribes of animals as the consequence of current events; such as one of those unusually long droughts to which South America is occasionally subject, when, as during the gran seco, which lasted three successive years, it was calculated that from a million and a half to two millions of animals died exhausted by hunger, the borders of all the lakes and streamlets in the province of Buenos Ayres being long afterwards white with their bones. The case of the dodo, a large and remarkable bird existing in the Mauritius during the early voyages to the East, appears to be a well-authenticated instance of the death of a species in comparatively recent times; and now of several races dangerous to man, or useful to him for their skins, it may be predicated that the period of their extinction is not very distant.

Of formations contemporaneous with the present era, an arrangement may be adopted which classifies them according to the agency immediately operating in their production. 1. Organic-coral reefs; peat-mosses or bogs; subterranean forests. Formations of coral-the agglutinated skeletons of departed races of coral animalcules, composed of carbonate of lime secreted from the ocean, with broken shells, echinites, and sand, all cemented together into hard calcareous rock- -are among the most interesting organic constructions of modern as of ancient times, now in course of augmentation from the living swarms. Detail here will be unnecessary, having previously referred at large to the islands which owe their origin to these marvellous creatures; and also to the submerged reefs advancing surely towards the surface of the waters, though at an excessively slow rate to us, which a slight submarine eruption might elevate into chains and clusters of islets, the agency undoubtedly which has uplifted some of the coralline formations of the Pacific thousands of feet above the deep. The island of Tahiti, composed almost entirely of volcanic rocks, has on the summit of its highest mountain a coralline stratum; a similar bed occurs in the Isle of France, between two lava currents; and all voyagers of modern date-Beechey, Quoy and Gaimard, Stutchberry, and Darwin-concur in the opinion that the coral reefs and islands proceeding in the Pacific do not go down many hundred feet below the surface of the waves, but rest upon submarine volcanic ridges and rocks. The cut in the next page represents species of three common genera of corals: Caryophyllia, the external character of the polyparium or stony skeleton of