74 EARLY MAN IN BRITAIN. [CHAP. iv. 



fathoms, which imply, that a land barrier was in that 

 position for a very long period. It would make but 

 very little difference to the Map of Pleiocene Britain if 

 we were to take the western coast-line to be marked by 

 the 300 instead of the 100 fathom line. 



It will be observed by the comparison of the Maps, 

 Figs. 6 and 10, that the geography of Britain in the 

 Meiocene age was modified in the Pleiocene only in two 

 important points the letting in of the Arctic waters into 

 the North Sea, and their free communication with the 

 Atlantic by the submergence of the area between the 

 Shetlands and Iceland. In other respects, Pleiocene 

 Britain was as it had been before, and plants and animals 

 could migrate over the dry land then uniting France, 

 Spain, and England together, without being confronted 

 by a physical barrier. A geographical continuity of this 

 kind in ancient times was considered by Professor Edward 

 Forbes l necessary for the presence of certain Spanish 

 plants such as Arabis ciliata and Pinguicula grandi- 

 Jlora in the south of Ireland. 



The Pleiocene mountains were similar to our present 

 mountains, but were undoubtedly higher, because of the 

 enormous amount of denudation which they have under- 

 gone in post-Pleiocene ages, as well as from their then 

 rising from a base at least 600 feet above their present 

 bases. The line of lofty volcanic cones, also, in the 

 Hebrides probably had not altogether lost their subter- 

 ranean fires in the early Pleiocene ages. Clusters of 

 small lateral cones or puys sprang up on their flank- 

 like those on Mount Etna, but they, too, were gradually 



i " Geological Relations of Fauna and Flora of the British Isles." 

 Memoirs of Geological Survey, i. p. 348. 



