290. Paleo-Geological and Geographical Maps of the British Islands. 
PLATE XO KOO ies le 
Interglacial Epoch. 
The Interglacial, or second, epoch of the Post-Pliocene period presents a remark- 
able contrast with that which preceded it. Instead of intense cold, there was a 
temperate climate similar to our own ; instead of elevation of the land, there was 
deep depression and extensive submersion beneath the waters of the sea; and 
instead of the formation of a glacial deposit like the boulder clay, there was the 
deposition of beds of sand, gravel, and loam, often containing sea-shells identical 
with existing species. The physical conditions of the two epochs could scarcely 
have been more different over the area here described, but this difference was by 
no means confined to the limited region of the British Isles. It extended, as Dr. 
Oswald Heer has shown, to Switzerland and the centre of Europe, and as Dr. 
Dawson has shown, to North America. 
The occurrence of an interglacial stage between two others of a glacial character, 
is admitted by most writers on the physical history of Post-Tertiary times.* The 
representative beds, or formations, have been recognised both in the west and east 
of England ; but some observers, including Dr. J. Geikie and Mr. 8. V. Wood, 
consider these threefold stages not to be representative of each other in time, but 
to some extent consecutive. This is a view which, upon careful consideration of 
the subject, I am satisfied is based upon good grounds. In the east of England, 
the consecutive deposits in succession to the Norwich Crag are so clearly and fully 
represented, that they enable us to trace the successive stages of the earlier glacial 
epoch, in a manner of which we have no where else a parallel. Agreeing with Dr. 
J. Geikie, that there are beds in Norfolk intermediate between the beds of the 
glacial epoch and the crag, not represented in the West of England, the following 
appears to be the succession, as made out by Messrs. 8. V. Wood and Rome, with 
their western equivalents. 
Representative Post-Phocene Serves. 
Lancashire, Cheshire, &c. East Anglia, 
Upper Boulder Clay, 5 . 5 ; Hessle Clay with Boulders. 
Middle Sands and Gravels (marine), ; Marine Gravels, giving place to littoral and 
fresh-water Gravels. 
eee Boulder Clay of Yorkshire. 
Lower Boulder Clay. Do. with Chalk. 
Great Chalky Boulder Clay. 
* Dr, James Geikie, ‘Great Ice Age,” 2nd edit., p. 328. Sir C. Lyell, “ Antiquity of Man,” 4th 
edit., p. 259-60. Dr. Geikie and Dr. Croll consider there were several interglacial stages ; but however 
this may have been in Scotland, only one can be recognised in England and Ireland with certainty. The 
more mountainous character and higher latitude of Scotland may account for many of the peculiarities of 
its glacial history. The changes from one set of conditions to another was doubtless gradual and slow. 
