S2 



Norfolk and Suffolk," which counties were submerged to an 

 extent of 400 feet below their present level. They think that 

 the Middle Glacial was kept out of this midland area by the 

 presence of the ice-sheet, and that it was only accumulated 

 beyond the limit of the land-ice by the currents which washed 

 its edge. 



All this, however, is so purely conj ectural, and though it might 

 account for some of the facts, yet it seems to create difficulties 

 so much graver than those which the authors seek to explain, 

 that it is impossible to take it as representing, with any degree 

 of probability, the actual physical conditions of the period. 



Admitting therefore that at present we cannot hope to 

 account for all the phenomena presented by the glacial deposits, 

 I am still inclined to think that a modification of the older 

 theory, and the supposition of a gradually increasing submerg- 

 ence from the date of the Forest Bed, offers the fewest difficulties 

 in explanation of their mode of occurrence. 



In this connection I would call attention to the claims of 

 coast-ice, recently advocated by Prof. J. Milne, to be regarded as 

 an important agent in glaciation. Such ice operates in less 

 depth of water than berg-ice, and is found to carry much 

 greater quantities of material; moreover it is capable of ex- 

 plaining the local character which the Boulder Clay almost 

 everywhere exhibits, and which has been thought a fatal 

 objection to the marine theory. 



Such a gradual submergence does not of course preclude the 

 possibility of there having been minor oscillations of level, and 

 changes in the amount of cold during the whole general period ; 

 but it would appear that the deposition of the Chalky Boulder 

 Clay marks the maximum both of depth and cold, and that the 

 land then gradually rose again from out of the glacial sea. 



Starting therefore with the supposition that at this time the 

 whole of Cambridgeshire was deeply submerged, let us consider 

 what would be the result of its gradual re-elevation. It is clear 

 that the clay-covered escarpment of the Chalk would first rise 

 as a low ridge, and would be subjected to the action of marine 

 currents ; these would sift and re-arrange the Boulder Clay, 

 forming deposits of gravel such as exist eastward, northward 

 and westward of the highest portions of the scarp. 



