Ixiv PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



the idea of a separate creation of the same series of Mammalia in and 

 for a small contiguous island cannot be entertained ; and that the 

 idea of their having swum across a tidal current of sea twenty miles 

 in breadth is equally inadmissible. 



I have thus endeavoured to trace the successive geological changes, 

 the upheavals and subsidences of the land, which by strong evi- 

 dence, botanical and zoological, have been shown to have occurred 

 in this western part of Europe during the more modern of the ter- 

 tiary periods. But we have not yet traced the more recent changes 

 which Professor Forbes points out in this essay, up to the historical 

 period. We have seen that most of our existing plants and animals 

 can boast a direct lineal descent from ancestors that flourished long 

 before man set foot on these islands, probably before the creation of 

 the human race ; certainly before the formation of the German 

 Ocean, or the English and Irish Channels, These seas have great in- 

 equalities of depth, but in some places the soundings are as much as 

 nearly 100 fathoms. They were probably formed by the double and 

 concurrent operation of subsidences of the land, and by the wearing 

 actionoftidesand waves on other parts of the land, cracked, fractured, 

 and loosened as it probably would be by these subsidences. We 

 know that the sea has worn away large tracts of land within our own 

 experience, and that lands on which forests of existing trees grew, 

 have subsided below the level of the sea, on many parts of our coasts. 

 " The formation of the German Ocean and Irish Sea, and new lines 

 of coast, events calling new influences into play, introduced the ex- 

 isting population of our seas. Part of our glacial testacea had been 

 extinguished, part retired to more congenial arctic seas, and a few 

 disappeared from the coasts of Europe, while they continued inhabit- 

 ants of the shores of America. A considerable number, however, 

 returned to the seas of their ancestors, where they became and re- 

 main the associates of numerous forms, some newly called into being 

 to people the new-formed seas, some coming with favouring currents 

 from the warmer seas of the south. Among the latter were a number 

 of forms which had not always been strangers to the British seas. 

 During the genial times preceding the glacial epoch, more than fifty 

 species of testacea, inhabitants at present of our seas, lived in them 

 whilst the Crag beds were in process of formation, but disappeared 

 under the chilly influences of the sub-arctic epoch which succeeded." 



On this post-pliocene plain, this upheaved bed of the glacial sea, 

 there must have existed extensive freshwater lakes, from the relics 

 we find of them. In Ireland and the Isle of Man, there are nume- 

 rous basins of freshwater marls resting on depressions of the upheaved 

 glacial sea-bed, containing shells of existing testacea, along with en- 

 tire skeletons and many detached bones and horns of the extinct 

 gigantic Irish Elk, the Megaceros Hibernicus, which in the opinion 

 of Professor Owen was the contemporary in our islands of the Rhi- 

 noceros, Mammoth, and other extinct mammalia, during the period 

 of the formation of the newest tertiary freshwater fossiliferous strata. 

 These freshwater marls are overlaid by peat with its included an- 

 cient forests, so that the time when the Megaceros lived was anterior 



