PLEISTOCENE CLIMATE AND MAMMALIA. 
397 
therefore be tolerably certain that the Pleistocene mammalia 
lived here at the same time that the glaciers still covered 
large areas in Great Britain and Ireland. 
The consideration of the Pleistocene climate is also inti- 
mately connected with the former extension of North- 
Western Europe into the Atlantic ; for the extremes of tem- 
perature implied by the mixed character of the former can only 
be satisfied by the view that Great Britain was not an island, 
but an integral portion of a continent. In the following map, 
which is based on that drawn by Dr. Petermann and published 
by Dr. Stieler, I have followed Sir H. de la Beche and Sir 
Charles Lyell in taking the 100-fathom line as representing 
the coast, the time from which the soundings deepen sea- 
wards so quickly in every direction, that the line of 200 
fathoms would include an area which is but slightly larger. 
As evidence of this coast line, Mr. Godwin- Austen has brought 
forward the littoral shells, the shingle, and the line of rocks 
which are found near the embouchment of what may be called 
the river of the English Channel. And that this river is no 
myth is proved by the discovery of the Unio pictorum , in from 
50 to 100 fathoms water, by Captain White, at the same 
point. 
To complete this very brief sketch of the physiography of 
Pleistocene Britain, I have inserted the rivers, and have traced 
them by the soundings to their mouths in the Pleistocene sea. 
A glance at the map will show the relation of the present 
rivers to those great arteries to which they once contributed 
their waters. It is obvious that the great valleys of the 
English Channel and the North Sea, and probably that of the 
British Channel, would afford free scope for the migration of 
the Pleistocene mammalia from France and Germany to our 
country, and that of the Irish Channel to Ireland. And 
it is by no means remarkable that the paleolithic savages 
who lived on the banks of the Somme or the Seine, or in the 
caves of Belgium, should have left like traces of their presence 
in the south and the east of England. Had they merely occu- 
pied one side only of what must have been to them a most 
valuable hunting-ground, and not sometimes have crossed over 
to the other, we should have cause to wonder at their caprice. 
EXPLANATION OF PLATE LXXVIII. 
Dotted Areas = those in which Pleistocene mammalia have been found. 
Lined „ = the extension of land to the 100-fathom line. 
Plain „ = Glaciers. Figures = fathoms. 
