INTRODUCTION. XXXI 



the remains of animals and shells of the land, river, and sea. 

 Certain parts of this area seem at length to have been 

 changed from sea into low marshy land, either because 

 the sea was filled up with sediment, or because its bottom 

 was up-heaved, or by the influence of both these causes."'' 



The present position of the fresh-water white marls in 

 Lancashire, in the Isle of Man, and in Ireland, in which 

 marls the remains of the Megaceros are so common, attest 

 the great changes which have taken place in the geo- 

 graphical condition of those lands since the period when 

 that now-extinct Deer left its remains in those newer 

 pliocene lacustrine deposits.* 



The extraordinary phenomena of the great northern drift 

 show that, whilst the eastern portion of England, and so 

 much of the western part as Mr. Murchison has called Silu- 

 ria,-\ were dry land, and inhabited by the pliocene Mam- 

 malia, the eastern part of Lancashire, nearly all Cheshire, 

 the north of Shropshire, and a large part of Staffordshire, 

 Worcestershire, and Gloucestershire, were under the sea. 



The indications of such changes, mighty in comparison 

 with any of which human history takes cognizance, pre- 

 pare us to view with less surprise the corresponding 

 changes which have taken place in our Mammalian Fauna ; 

 but we are still ignorant of the cause of the extirpation 

 of so large a proportion of it as has become extinct. It 

 is an important fact, however, that a part and not the 

 whole of the terrestrial species have thus perished, : whence 

 it may be concluded that the cause of their destruction has 

 not been a violent and universal catastrophe from which 

 none could escape. There is no small analogy, indeed, 



* Professor Ed. Forbes, cited at p. 467. t ' Silurian System, 1 4to. p. 523. 



J This fact was established by several of the determinations in my ' Reports 

 on the British Fossil Mammalia,' communicated to the Meetings of the British 

 Association in 1842 and 1843. 



