302 JOSEPH PRESTWICH^ F.U.S., P.G.S., OX A POSSIPLE 



during a period wliicli geologists have agreed to consider as one 

 and indivisible, the oscillations have been great, both of depression 

 and elevation, and that there has been at several distinct peinods 

 a constant return to a level very near the present one." (Quart. 

 Journ. Geol. Soc. vol. vii, 1851, pp. 130, 136). Later, Mr. 

 W, A. E. Ussher in the same journal (vol. xxxiv, 1878, pp. 52, 

 454), and Pi-ofessor James Geikie (Frehidnric Europe, 1881, pp. 

 224-227), have presented a similar opinion that the " head " or 

 rabble drift was a subaerial deposit, belonging to the time of the 

 Glacial period, and that this ai-ea was then uplifted several 

 hundred feet, uniting Great Britain with the continent, though 

 not, as they suppose, to so great altitude as had been suggested by 

 Mr. Godwin- Austen. His early discussion of this question, similar 

 conclusions for North America stated in Prof. James D. Dana's 

 presidential address before the American Association in 1855, and 

 a paper by Mr. T. F. Jamieson in the Quarterly Journal of tht^ 

 Creological Society (vol. xxi, 1865), clearly recognised not only 

 o-reat epeirogenic uplifts of drift-bearing areas, which, at their 

 culmination bringing a cool high plateau climate, I think to have 

 caused the Ice-age, but also the ensuing subsidence of the ice- 

 burdened lands, which appears to have induced the rapid final 

 melting of the ice-sheets. 



The brevity of this time of uplift in southern England is well 

 shown by the rabble drift, which was preceded and followed by 

 slight submergence, and the formation of beaches that are now 

 raised somewhat above the sea level. We thus have an excellent 

 confirmation of Professor Prestwich's opinion that the Glacial 

 period was geologically short, and not many thousands of years 

 ago. In more northern regions the extensive preglacial erosion 

 of the fjords implies that the gradually increasing uplift there 

 occupied a far longer time, probably having begun during the 

 Tertiary era. 



THE AUTHOR'S REPLY. 



August, 1894. 

 Professor Prestwich writes to express his regret at not having 

 been present to reply in person to the criticisms of his friends. 

 They have however made his task an easy one. In answer to Sir 

 Henry Howorth, he would observe that he does not postulate a 

 great Submergence in order to produce the phenomena he has 

 described, but he deduces from the character of the phenomena the 

 conclusion that the whole of the area in question has been affected 

 by a common cause, and exhibits resulls which indicate that they 

 had a common origin. The JJilnvmm gris of French geologists 



