78 Dr. James Geihie — Preservation of Deposits under 'Till.'' 



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 fragments 

 of what must have been widely extended deposits covering a broad 

 region, from which they have since been entirely removed. 



Mr. Hinde tells me also that he has just discovered 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 full of striated stones, 

 — six feet thick. The interesting point about this section is the 

 occurrence of plant-remains in beds that belong to Dr. Newberry's 

 " laminated clay series " — a series which that able geologist has 

 described as unfossiliferous, and never overlaid by Till. 



I might easily refer to many examples of similar phenomena in 

 the glaciated districts of Northern Europe, to show that the distri- 

 bution of interglacial beds is the same there as in our own country 

 and North America. But I need not enter further into details at 

 present. It is enough for my immediate purpose to have again 

 pointed out that, in considering the origin of glacial and interglacial 

 deposits, it is needful that we pay more attention to the distribution 

 of these beds than we have hitherto 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 preconceived 

 notions of what Nature's forces can and cannot do are often enough 

 wide of the mark.' 



It is needless to refer one to the petty glaciers of the Alps and 

 Norway to prove that glacier-ice cannot both erode its bed and 

 accumulate debris upon that bed at one and the same time. A 

 mountain- valley glacier is one thing — a glacier extending far into 

 the low grounds beyond the mountains, and, it may be, coalescing 

 with similar extensive ice-flows, is another and very different thing. 

 No considerable deposit could possibly gather below alpine glaciers 

 like those of Switzerland and Norway ; but underneath glaciers of 

 the kind that invaded the low grounds of Piedmont and Lombardy 

 we know that thick deposits of tough Boulder-clay, crammed with 

 scratched stones, did accumulate ; and not only so, but that tliese 

 glaciers flowed over incoherent deposits of sand and clay containing 

 marine shells of late Tertiary age, without entirely obliterating them. 



1 It may reasonably be doubted whether interglacial deposits were always so very 

 loose and incoherent at the time they were overridden by ice. My brother has 

 suggested that when the ice-sheet advanced over a land-surface, the loose superficial 

 deposits might be frozen so hard as to be capable of resisting a very considerable 

 degree of glacial erosion. 



