294 PREHISTORIC EUROPE. 



these interglacial clays, etc., appear to occur only in the lake- 

 depressions and other localities at low levels. I cannot find 

 them in the more elevated district, and supposing a fresh glacier 

 now to creep over this country, it would sweep before and 

 beneath it the till on the uplands, and cover over the stratified 

 clays in the present lakes with this material ; and there would 

 thus be a repetition of the same arrangement of stratified beds 

 and overlying till as is now seen in the present cliffs facing 

 the lake." He thinks that the earliest ice -sheet had more 

 grinding power than the ice-sheets of later cold periods ; but 

 the till that overlies the fossiliferous interglacial beds indicates, 

 nevertheless, the former presence of a very considerable ice- 

 sheet, for the beds which it has spared are the mere frag- 

 ments of what must have been widely extended deposits cover- 

 ing a broad region, from which they have since been entirely 

 removed. 



Mr. Hinde tells me also that he has detected plant-remains 

 in a similar position near Cleveland, Ohio. The deposits at this 

 place are described by Dr. Newberry as his " pebbly Erie clay." 

 They consist, my correspondent says, first, of till at the lake- 

 level ; secondly, of about 48 feet of sand and loam, containing 

 a layer of plants ; and thirdly, of good unstratified till, 6 feet 

 thick, full of striated stones. 



I might easily refer to many examples of similar phenomena, 

 but I need not enter further into details. It is enough for my 

 immediate purpose to have pointed out that, in considering the 

 origin of glacial and interglacial deposits, it is needful that more 

 attention be paid to the distribution of these beds than has 

 hitherto been done. This is the direction in which, as it seems 

 to me, we must look for the key to the whole mystery ; indeed, 

 I do not see how otherwise we are to arrive at any reasonable 

 explanation of the phenomena. At the first blush it may appear 

 hard to believe that a great mass of solid ice could ever pass 

 over the surface of incoherent deposits of clay and sand. But 

 the appearances presented by these deposits tell their own tale, 

 and teach us, as we have been taught before, that our precon- 



