440 Climate of the Glacial Period. (October, 
northern species of mollusca, such as Cyprina islandica and 
many others. In Southern Sicily a magnificent series of 
shells have been preserved in rocks rising 2000 feet above 
the sea. Amongst the latest of these deposits, the northern 
forms of mollusca appear, and they are nowhere accompanied, 
followed, or immediately preceded by these tropical species 
that we ought to find if Mr. Croll’s theory be true; to obtain 
them we must go back to Early Tertiary times, to the Miocene 
and Eocene periods. ‘These alternations of climate cannot 
have taken place; it is not possible that all memorials of 
Arctic faunas and floras in the Eocene and Miocene periods, 
and all the remains of tropical species in the Glacial period 
could have been destroyed, whilst in the former case the 
southern forms, and in the latter the northern, were abun- 
dantly preserved. And yet, strangely enough, we are told 
by the advocates of this theory that it is in harmony with 
geological facts. + 
Coming down to post-glacial times, we have in the marine 
shells only evidence of a gradual amelioration of the climate. 
Some of the freshwater beds are, however, supposed to indi- 
cate that, immediately after the Glacial period, a warmer 
climate prevailed than we enjoy at present. They only, 
however, show that it was a more Continental one, which is 
in accordance with other facts indicating that the British 
Isles were then joined to Europe by continuous land. I 
have published my reasons* for believing that a great river, 
into which flowed the waters of the Rhine, the Thames, the 
Seine, and many other streams, ran southwards, through 
what are now the Straits of Dover and the English Channel, 
as far as, and possibly further than, the Bay of Biscay, ata 
time when the level of the sea stood much lower than at 
present. The ice of the Glacial period had then retired from 
the southern portion of the bed of the German Ocean, but 
the flow of the waters northwards was still stopped by it, or, 
as I now think more probable, by the great moraines left 
across the ocean bed by it. Mr. Godwin-Austen has, in his 
various classical papers on the post-tertiary beds of the 
British Channel, shown the great probability that the Straits 
of Dover did not exist until after the Glacial period, but that 
a neck or isthmus of land stretched across, joined England ~ 
to the Continent, and divided the German Ocean from the 
English Channel. Now, at the height of the Glacial period, 
we know that the greater part of the bed of the German 
Ocean was filled with ice, that stretched from Scandinavia 
* Nature, vol. x., p. 25. 
