98 



several centres of ice action ; that the Scandinavian mountains 

 sent out huge streams that flowed in one continuous sheet into the 

 Baltic, invading North Germany, and spreading along the floor of 

 the North Sea until it coalesced with the land ice proceeding from 

 the various mountain groups of the British Isles, till at last, with 

 the possible exception of portions of high ground, Scandinavia and 

 Britain, with part of Germany, were enveloped in the same shroud 

 of ice. Were this the case — and the evidence is very strong — and 

 we grant that boulder clay forms beneath the ice and is carried 

 along with it, at the warm latitude where the latter melted, there 

 would have been prodigious accumulations of debris, gathered 

 indiscriminately from the Arctic Circle, Scandinavia, and Britain : 

 but none such exist. What then became of the Scandinavian 

 debris, if it did not intermingle with the spoils of the British 

 Islands 1 



In this hasty review of some of the main features of glacial 

 action, our chief impression must be how little we know, and in 

 what numberless directions research may be made ; but we have 

 chiefly considered matters which refer either to distant ages, or to 

 far off lands, which are beyond our observations. Let us now 

 examine the boulder clay formation as we find it in our own day, 

 the product of forces we are not yet able to explain, and about 

 whose origin, though amongst the newest of geological records, we 

 know less than of some of the most ancient of rocks. The boulder 

 clay varies in colour and composition, according to the general 

 characteristics of the neighbouring hills, but its mode of occurrence 

 seems fairly constant. It consists of either one or two beds of 

 true boulder clay, with various deposits of sand and gravel. The 

 lower beds are usually more compact than the upper ones, and 

 more highly charged with stones; but this is not an invariable rule. 

 Occasionally sections occur where a greater or less thickness may 

 be seen, where there is little clay except in the interstices of what 

 appears a compressed mass of stones. There are, however, 

 no characteristics which definitely indicate respectively what are 

 termed by the Geological Survey the Upper and Lower Boulder 

 Clays; and in the memoir for South-West Lancashire, it is acknow- 



