June, 1892. 
THE ICE AGES, PAST AND FUTURE. 
121 
ON THE ICE AGES, PAST AND FUTURE, AND 
THEIR CAUSES.* 
BY W. P. MARSHALL. 
There is irresistible evidence of an Ice Age having existed 
at some former period, in which this country, with the 
northern portion of Europe and America, was covered by a 
continuous ice sheet of great thickness. This covered all 
Scotland and the greater portion of England, and there 
is distinct evidence that the portion of the country where we 
are now living was at one time completely buried under 
a continuous mass of ice. In the accompanying map (Plate 4), 
for which I am indebted to the kindness of Dr. Lapworth, 
the shaded part shows the portion of the country proved thus 
to have been glaciated, extending southwards from Birming¬ 
ham to half-way between Worcester and Gloucester, to the 
extremity of South Wales on the west, and nearly as far 
south as London on the east. 
The evidence of this Ice Age is of two kinds. First, the 
presence over a large extent of the country, towards the 
southern boundary of the shaded area, of great numbers 
of boulders —fragments of rock of various sizes up to several 
feet in diameter, which are totally distinct from the strata of 
the locality, and have been identified by careful examination 
as fragments of the mountains of Wales, Cumberland, and 
Scotland. These are indicated on the map by lines from five 
different centres:— 
Mid Wales. from 
Arenig (Snowdon district) 
Eskd^le (Cumberland) 
Lake District (Helvellyn) 
5 5 
5 > 
50 miles distance, grits. 
80 „ 
,, felstones. 
120 „ 
,, granites. 
180 „ 
,, felsites and 
granites. 
170 „ 
,, granites. 
on the east 
coast that are 
Criffel (Dumfries, Scotland) ,, 
Boulders are also found 
considered to have been conveyed from Norway. 
There are no intermediate sources from which these 
boulders can have been obtained, and there is no other known 
means of transport for these blocks than conveyance upon a 
glacier. Fragments of exposed rocks split off by frost action 
or otherwise and falling upon a glacier, rest upon the surface 
and are carried forward, slowly but continuously, by the 
constant gradual flow of the glacier down from the higher 
* Read before the Birmingham Natural History and Microscopical 
Society, May 17th, 1892. 
