526 REV. R. B. WATSON ON THE GREAT DRIFT-BEDS WITH SHELLS 



fixed, that in the water-worn gullies one may often climb far up the steep Lank 

 by holding on to them. On the whole, it is perhaps less compressed and homo- 

 geneous than boulder-clay often is ; it is also occasionally traversed by bands of 

 stones or beds of sand and clay. Towards its upper surface it is often somewhat 

 disintegrated, and less dense than below. At times it passes upwards into a dense, 

 fine gravel. In some places it is to be found resting directly on the rock below ; 

 but at the lower levels it is often separated from the rock by a bed of sandy clay, 

 while at a higher level it is, in at least two instances, underlain by a very hard, 

 densely-packed, angular gravel or coarse sand, with large striated boulders, which 

 seems to have lain directly under a glacier. 



Shells occur occasionally in considerable quantities, both in the boulder-clay and 

 in the sandy clay (not in the glacier gravel) below, at various heights, from 80 to 

 320 feet above the sea. No general principle explanatory either of the presence or 

 absence of the shells is obvious, except that they seem uniformly wanting in 

 the beds of large stones. In the boulder-clay they are very much broken. In the 

 laminated beds, both those which rest on the rock and those which traverse the 

 boulder- clay, the shells, when present, though of more delicate type, such as 

 Ledas Naticas &c., were less destroyed. At first, from the broken state of the 

 shells, I thought the whole deposit must have been formed on the beach ; but 

 more careful observation showed that the inference was drawn merely from bits 

 washed out by the rains, these being by far the most abundant. If carefully dug for, 

 the shells may often be found, crushed indeed, yet with each fragment in its own 

 place — two-shelled species with their valves united. Some of the large speci- 

 mens of Cyprina, though unbroken, are indented as by a sudden violent blow. In 

 short, the whole condition of the shells suggests that heavy stones have been 

 dashed down on them, or that they have yielded in the bed where they lay to the 

 weight of sand and stones more quietly piled over them. 



Of species there are sixteen determined and one doubtful, besides many frag- 

 ments which do not seem to belong to any of these, but are too minute for re-" 

 cognition.* 



As to their habitats, they belong distinctivel}'^ to the coralline zone, or to even 

 deeper water. Of the sixteen species which have been determined, seven, so far 

 as they are known on our coasts, are never found in water shallower than 150 

 feet (25 fathoms) ; and except one, all the others, though found at a less depth, 

 are also found in very much deeper water. The single exception was the Litorina 

 litorea, but of it I found only two fragments. 



In character, Mr Searles Wood, who was good enough to examine them forme, 

 pronounces them decidedly boreal. All the species, except Turritella communis 

 (which is common in the Norwegian drift-beds), extend to the arctic province. 



* For list of these see end of paper. 



