AND EIVER VALLEYS BOEDEEING THE BRITISH ISLES. 313 



It will be observed that as compared with the British sub- 

 coastal features there is a general resemblance, but with one 

 important exception, namely, the absence of the representa- 

 tion of the " Blake Plateau." We may, without hesitation, 

 recognise our British platform as the equivalent of the Con- 

 tinental shelf ; but as I have already shown, this terminates 

 along the margin of one great escarpment descending to 

 depths of 8,000 or 9,000 feet. A soHd escarpment of this kind 

 indicates a slow continuous elevation, after the British plat- 

 form had been planed down by wave action, and subsequent 

 depression after a long lapse of time. On the coast of the 

 American continent, however, there appears to have been an 

 intermediate period representing a pause in the process of 

 elevation and subsequent depression, during which the second 

 shelf, or "Blake Plateau," was elaborated. In all cases, 

 however, it must be remembered that the formation of these 

 escarpments was mainly due to wave action, undermining 

 the cliifs during prolonged pauses in the process of elevation 

 or subsequent depression. 



VII. Geological Age of the Submerged Features. — The forma- 

 tion of the British platform, like that of the American " Con- 

 tinental Shelf," may be referred back with confidence to the 

 Mio-phocene period, and that of the grand escarpment to 

 the succeeding early Pleistocene or Glacial stage. This view 

 is in harmony with analogy and what we know of the 

 physical conditions of these periods. The Mio-pUocene 

 stage was one of great terrestrial changes of land and sea 

 over the European and adjoining areas; but the climatic 

 conditions were warm and genial, with a foretaste of more 

 rigorous conditions towards the close. An elevation of 100 

 to 200 fathoms round our coasts would have been insufiicient 

 to have brought on glacial conditions, although undoubtedly 

 tending in that direction in our more mountainous districts ; 

 but a further elevation to the extent of several thousand feet 

 would undoubtedly bring about such conditions ; and we are, 

 therefore, justified in inferring a close relationship between this 

 latter rise of the land, with the adjoining oceanic bed, and the 

 incoming of those Arctic conditions which resulted in covering, 

 not only our mountain heights with perennial snow and 

 glaciers, but also the adjoining plains. 



Having already in my former paper treated the subject of 

 the origin of the Glacial period at some length, it is unneces- 

 sary that I should dwell upon it here — or explain how the 

 great rise of the land would necessarily result in bringing 



