ARCTIC CHARACTER OF FOSSIL SHELLS NO PROOF OF FORMER GLACIERS. 551 
posits, whether on the summit of Moel Tryfane at heights of 1700 feet above the 
sea, or in the lower country of Shropshire at heights of 300 and 400 feet. In all 
other cases around Snowdon as well as on Schehallion, therefore, we, for our parts, 
can see nothing more than may be completely explained by the transmission of 
massive bodies of detritus, which derived from the higher parts of those mountains 
at the periods of their elevation, would necessarily, we contend, have produced 
exactly the same appearances as if a heavy incumbent glacier had traversed them 1 . 
The coarse drilt of the British geologist, or the osar of the Swede, are no imaginary 
creations. They are enormous banks and ridges of stones which have usually 
undergone great friction, are associated with clays and sands, sometimes finely 
disposed, at other times tumultuously arranged, as if by water, and among them, 
whether in Sweden, Denmark, England, Scotland or Ireland, are occasionally found 
sea shells. Why then are glaciers, although doubtless they are and have been 
“ verse causse” of sti'iation, in countries where very high mountains are in evidence, 
— why, we ask, are they to be forced upon us as the sole means of solving this 
problem, in regions where no such features exist ? and why in such low situations 
are we not to infer, that the drift has done the same work as the glacier has per- 
formed in the lofty Alps ? 
But some of the very marine shells on which we have been insisting as proofs of 
the aqueous formation of this boulder drift, are said to be Arctic species, and have 
therefore been quoted as indicating the prevalence of a colder climate in our lati- 
tudes in those days than at present 2 . Hence glaciers, it is supposed, may have been 
adjacent to such arctic animals. But what are the species of shells associated with 
the great boulder drift in Denmark ? why in many tracts the very same which now 
1 This explanation applies equally to Killarney and all the other cases cited. 
4 We were, at one time, disposed to think, that the presence of sub-fossil shells of Arctic character 
naturally indicated the former presence of a much colder climate in those latitudes where they have been 
found (see Proceedings of Geol. Soc., vol. iii. p. GS0). But independent of discoveries in submarine 
life -we now hold that it is unnecessary to have recourse to such an argument, in relation to any phe- 
nomena in the British Isles or similar latitudes ; for we can easily imagine, that when very different 
physical features prevailed, and when lands now above the sea were beneath it, cold currents may have 
extended very far southwards of the arctic circle, and have been inhabited by species now restricted 
(through geographical changes) to a less horizontal range. Again, we then believed, that no great erratic 
blocks had ever been seen in equatorial or intcrtropical tracts, but we learn from the last researches of Sir 
Robert Schomburgk in British Guiana, that enormous boulders of far-transported crystalline rocks are 
there found on the surface of the sedimentary deposits of the plains and slopes, — a region in which no 
ice or glaciers can ever have existed (see memoir read before the Royal Geographical Society of London, 
which will appear in the 15th volume of the Journal of that body). 
4 B 2 
