380 NATURAL SCIENCE [December 



Caspian and Aral with the White Sea and the Baltic, thus forming 

 an effectual barrier to the westward course of the mammals. The 

 existence of such a sea is supported by the presence of arctic forms 

 of life in the Caspian, and the occurrence of the Caspian mollusc 

 Dreyssensia polymoiyha in the Lower Boulder Clay of Germany. As 

 this central European sea was replaced in part by a land surface, 

 the way was opened for the Siberian mammals to pass on into 

 western Europe. Now we are confronted with the startling fact that 

 the British deposit in which these mammals first appear is the 

 Forest Bed, usually considered the newest member of the Pliocene 

 series. Are we to suppose, Dr Scharff asks, that the animals made 

 their way into England by Asia Minor, Greece and ►Southern 

 Europe, and so reached our shores before Central Europe was open 

 to them ? That part of the older southern fauna — the ' South- 

 Central ' section — travelled into Western Europe by this route from 

 Siberia during Pliocene times he does believe. But, he argues, it 

 is impossible that the true ' Siberian ' animals could have passed 

 that way, seeing that their remains are entirely absent from South 

 European, as well as from Irish, Scottish and Scandinavian, deposits. 

 He is therefore driven to the conclusion that the Forest Bed and 

 other British deposits usually classed as Newer Pliocene must be 

 considered as rather later than the Lower Continental Boulder Clay, 

 and reckoned to be of Pleistocene age. In support of this correla- 

 tion he also brings forward the presence of arctic shells in the newer 

 crags. 1 



Having thus fixed the period when these Siberian mammals 

 appeared in England, Dr Scharff believes that he has obtained the 

 latest possible date for the ' last link ' of the land-connection be- 

 tween England and Ireland. For if the way into Ireland remained 

 open long after these mammals reached English territory, what can 

 have prevented their onward course to the western island ? The 

 wide range of the mammals as compared with the restricted range 

 of the invertebrates of the same faunistic section has been dwelt 

 upon in the opening part of this paper. It is certain that the vast 

 number of widespread invertebrates that inhabit Ireland as well as 

 Great Britain must have passed over the Irish Se,/ when it was a 

 lake and river valley, or crossed the later northern isthmus which 

 joined northern Ireland to south-western Scotland. But as the 

 Siberian mammals were kept out of Scotland by the Pleistocene sea, 

 this northern isthmus may be left out of reckoning as far as they 

 are concerned. If the slowly-moving army of spiders, beetles, snails 



1 The reader is referred to Dr ScharfFs paper for the numerous references supporting 

 these positions. It will he seen that the editorial statements of Dr SchartFs views 

 {supra, p. 224, "that the lower continental boulder clay is Pliocene . . . that the 

 Siberian mammals migrated into Western Europe to the south of this sen ") convey the 

 exact reverse of the opinions really advocated by the author. 



