INTRODUCTION. XXX1 
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 A/egaceros 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 St/u- 
ria,f 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. + ‘Silurian System,’ 4to. p. 523. 
+ 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. 
