AMONG GLACIEES EECENT AND EXTINCT. 
181 
the great Secondary reptilia, and the ammonites and scaphites, 
which swarmed in the cretaceous seas, should not have lived on 
to the days of the Tertiaries. It is very easy to say “ they died 
out,” hut there must be some cause for 44 the dying out,” and it 
would be satisfactory if we could arrive at some conclusion as 
to the reason why ! Now we can easily conceive that recurring 
glacial periods must have a considerable effect upon the life of 
the period, especially when affecting latitudes where for long 
ages the animals and plants had been adapted to a moderate 
instead of an Arctic climate. Some species might never 
become sufficiently adapted to bear the change, however 
gradual, and, incapable of migration, would perish for ever, 
leaving only their fossil relics to testify of their former ex- 
istence. Still, whether these periodical changes of climate, 
after the lapse of hundreds of thousands of years, have occurred 
or not, all will perceive what an effect Frost must have had 
upon that part of the globe which we inhabit, during the 
Glacial Epoch, and which certainly and assuredly once affected 
large tracts of country in Europe and America. 
A large part of the northern hemisphere covered either by 
ice like that of Greenland, or by great snowfields and vast 
glaciers ; great herds of animals of various kinds driven 
towards the south for bare life and sustenance ; seas frozen 
where now the white sail quivers in the wind ; rivers bound 
like iron where now the steamer dashes the waters from her 
prow ; great cities, such as Edinburgh, whose sites were scored 
by the ice, or grooved by the glacier, or, like the cathedral 
towns of Gloucester, Bristol, and Worcester, were rolled over 
by the waters of iceberg-traversed seas — these are no small 
changes belonging to the history of the land we live in, and 
were the effects of Frost. 
And I may take the opportunity of stating that the more I 
study glacial phenomena in various parts of Europe, the more I 
am impressed with the belief that the last phase of the Glacial 
Period, in this country at least, was a period of the return of 
; glaciers in the Highlands, accompanied by great falls of snow 
on the lower hills, and over Great Britain generally. The 
melting of this snow, accompanied by a great summer rainfall, 
producing floods and fresh-water currents, was, I think, the 
great agent which carried down the gravelly debris which 
constitutes the angular detritus which is so widely spread 
over large areas. The same streams, too, which spread out this 
superficial debris no doubt also washed out of position many of 
the earlier marine drifts and gravels, and stranded them at a 
lower level. At the meeting of the British Association held at 
Birmingham (1865) I endeavoured to uphold these views as 
applied to the last and overlying drifts of the regions of 
