of the tertiary period northern Asia was probably almost entirely under water, and a broad tract of shallow sea may have extended, broken only by a few islands, from the latitude of 50° north to the North Pole. A chain of islands, nearly continuous, may then have existed in what is now the North Pacific Ocean, bringing the islands east and south of the Philippines into close relation with Australia, and with the archipelagos extending many hundred miles to the east of that continent, while Australia may also have then extended westward and northward between the tropics. A considerable part of southern India was no doubt covered by the sea; but land extended probably towards the east and west from central India, perhaps connecting Arabia with the peninsula of Malacca. Within this broad tract of land there appears to have been, during a great part of the tertiary period, a very extensive fresh-water lake, whose northern shore extended within the temperate zone; and on the banks of this lake lived vast herds of the larger Mammalia of all kinds, with those other animals characteristic of the old continent and the tertiaries of India, whose remains are so abundantly distributed in many distant regions. The disturbances which were then in action breaking up the chalk in England and elevating the Weald; those which, advancing eastward, formed hills in the great Alpine countries of Europe; those which also lifted the Caucasus from the sea-bottom, and partly found vent in the now extinct volcanoes of Asia Minor, had not yet disturbed this vast and thickly-peopled district, which was not greatly modified till very late in the tertiary epoch.

The Himalayas, and the mountains which now connect that chain with Persia, were, however, it is probable, even then indicated by a chain of islands, and did not till a much later period become elevated into a mountain range. The sands and other rocks, which, by slight undulations of the surface, had been deposited in great thickness on what are now the flanks of this range, and which received and buried vast multitudes of the bones and other remains of the inhabitants of the land, were then lifted up, and partook both of the main elevatory movement which lifted the plains of India, and of the local disruption which produced the mountain chain.

The elevation which commenced in the Himalayan region did not at once disturb the formation of deposits a little further to the south. These seem to have been continued without interruption far into what may be considered the modern period; and yet, after these, there occurred changes in this part of the world of the most gigantic nature, resulting in the outpouring of vast quantities of lava, and the elevation of the singular chain of the western Ghauts of India. Scarcely any distinctly marine deposits of a late tertiary period have yet been recognized in this part of the world.

These movements, described in so few words, were doubtless going on for many thousands and tens of thousands of revolutions of our planet. They were accompanied also by vast but slow changes of other kinds. The great plains of Tartary, the whole of Siberia, and many parts of north-western Europe, were then undergoing elevation. The inhabitants of a tropical or warm temperate continent extended into

these new countries, becoming acclimatised in high northern latitudes; and where we now find only the bear, the wolf, and the fox, the elephant, the rhinoceros, the hippopotamus, and a multitude of feline and other typical carnivorous species, were then fully represented. As, however, the northern land increased in extent, rose in elevation, and advanced further towards the pole, the effects of such change became felt. Intense cold advanced further to the south, the climate of the central districts from insular became extreme and continental, and at length the greater number of the animal inhabitants, unable to exist under such circumstances, gradually, but completely died out.

Meanwhile we may inquire concerning the fate of the continent whose position between the tropics has also been indicated. The expansive force employed in lifting up, by mighty movements, the northern part of the continent of Asia, found partial vent, and from numerous subaqueous fissures there were poured out the tabular masses of basalt occurring in central India, while an extensive area of depression in the Indian Ocean, marked by the coral islands of the Laccadives, the Maldives, the great Chagos bank, and some others, were in course of depression by a counteracting movement.

A similar area of depression, on a far grander scale, is also indicated among the western islands of the North Pacific Ocean, and we see distinct proof of great change having been effected in all these districts; involving, indeed, not only depression, but partial and occasional elevation, especially in the line of modern volcanic action extending from Sumatra to New Zealand.

The continental area formerly, it would seem, connecting the island of New Guinea with parts of Australia, and reaching to about 10° N. lat., seems to have sunk down, contemporaneously with the elevation of land in the north temperate zone; and the movement of depression in this case, and of elevation in the other, is most probably not yet completed. During the changes thus going on, it is not easy to conjecture at what rate other and corresponding changes may have affected the organic world, but one series of facts seems distinctly made out, and forms the groundwork on which these conclusions are based. I mean the former distribution of the larger land animals in groups not very dissimilar to those now existing over certain districts, and analogous to those at present connected by broad physical characters. This arrangement of the groups corresponds also remarkably, and in a most interesting manner, with the differences observable between the generic forms which were then common and those that are now met with. It agrees in the singular fact, that many of the groups of species formerly represented by gigantic types were not confined to one district, but extended over all the known land of the eastern hemisphere. It agrees also with the arrangement of nearly allied species at the present day, many of these being indigenous in distant and unconnected spots now, and having been so formerly. And, lastly, it proves that there is as little evidence to be derived from this branch of geological investigation, as there is from recent zoology and botany, in favour of any view of local or secular development of new typical forms of organic existence; since these modifications are rather

produced at once in distant spots, which, so far as we know, were as unconnected formerly as they are at present.

The distribution of the more characteristic land animals in groups is the main fact to be observed in considering this part of the subject; but we should not forget that some important set of causes must also, in all probability, have been in action, tending to produce that singular development of the larger quadrupeds, which has not only peopled the continents and islands of the Old World with gigantic types, but has also affected America, in the southern as well as the northern districts. In that part of the world, as elsewhere, there is a detached and singular group of animals, now greatly limited in distribution, but anciently represented by a large number of individuals as well as species, attaining dimensions not less gigantic in proportion than those of the elephantine monsters or reptiles of India or western Europe, or even of Australia and New Zealand.