Revieivs — Prof. A. Geikie's Geological Sketches. 323 



that produced the isolation of Britain. The whole area slowly sank, 

 until the lower tracts were submerged, the last low ridge connecting 

 the land with France was overflowed, and Britain became a group 

 of islands" (p. 359). Before this separation and — "previous to the 

 final retreat of the Ice, the alternating warmer intervals brought 

 into Britain many wild animals from milder regions to the south. 

 Horses, stags, Irish ' elks,' roe deer, wild oxen, and bisons roamed 

 over the plains ; wild boars, three kinds of rhinoceros, two kinds 

 of elephant, brown bears and grizzly bears, haunted the forests. 

 The rivers were tenanted by the hippopotamus, beaver, otter, and 

 water-rat ; while among the Carnivora were wolves, foxes, wild cats, 

 hyaenas, and lions. Many of these animals must have moved in 

 herds across the plains, over which the North Sea now rolls. Their 

 bones have been dredged up in hundreds by the fishermen from the 

 surface of the Dogger Bank "^ (p. 357). 



Professor Geikie thinks that previous to this the flora of colder 

 latitudes, together with the accompanying reindeer, musk-sheep, 

 lemming, Arctic fox, glutton, and other northern animals had 

 retreated from our low grounds (p. 356) ; but this could hardly 

 have been the case ; for in the Thames Valley deposits the remains 

 of these high Arctic forms lie commingled in the same set of deposits 

 with those presumably from lower latitudes ; as if this region had, 

 at that time, served as the meeting-place of faunas now geographically 

 remote, but which then, had a far wider area of distribution. 



To return, however, to the discussion of the isolation of Britain. 

 " Unquestionably the isolation was helped by the ceaseless wear and 

 tear of the superficial agencies which are still busy at the same task. 

 The slow but sure washing of descending rain, the erosion of water- 

 courses, and the gnawing of sea- waves, all told in the long degrada- 

 tion. And thus, foundering from want of support below, and eaten 

 away by attacks above, the low lands gradually diminished, and dis- 

 appeared beneath the sea. 



" Now, in this process of separation, Ireland unfortunatelj'- became 

 detached from Britain. We have had ample occasion in recent years 

 to observe how much this geological change has affected our domestic 

 history. That the isolation of Ireland took place before Britain had 

 been separated from the continent may be inferred from a comparison 

 of the distribution of living plants and animals. Of course, the 

 interval which had then elapsed since the submergences and ice- 

 sheets of the Glacial period must have been of prodigious duration, 

 if measured by ordinary human standards. Yet it was too short to 

 enable the plants and animals of Central Europe completely to 

 possess themselves of the British area. Generation after genera- 

 tion they were moving westward, but long before they could 

 reach the north-western seaboard, Ireland had become an island, so 

 that their further march in that direction was arrested, and before 

 the subsequent advancing band had come as far as Britain, it too had 

 been separated by a sea channel which finally barred their progress. 

 Comparing the total land mammals of the West of Europe, we find 

 that while Germany has ninety species, Britain has forty, and 



