Geological Society. 521 



to the same great phj^sical forces, glacial and diluvial, under much 

 colder conditions of the northern hemisphere than prevail at present ; 

 and this apparently at a time intermediate between the extinction of 

 European and American elephants by cold, and the creation of the 

 human race. We have not yet, hovt^ever, sufficient materials for the 

 full admeasurement of the amount of influence which has been ex- 

 ercised by ice in its various forms upon the surface of the globe, and 

 the following are important desiderata. With respect to elongated 

 ridges and tumuli of gravel, it remains to discriminate how far they 

 may have been derived from, or modified by, the action of ice under 

 one or more of the three following conditions: 1. Were they lodged 

 by glaciers alone, without the agency of water, in the form of mo- 

 rains on their flanks and front? 2. Have they been stranded by 

 icebergs loaded with gravel upon the shores of lakes, or estuaries, 

 or seas ? 3. Have they been dropped in deep water by floating and 

 melting icebergs, and re-arranged by whirlpools and conflicting cur- 

 rents in the form of oblong reefs and groups of obtuse cones which 

 they actually present? Another large field of inquiry must be 

 forthwith entered upon, in the distinctions we shall have to make 

 between raised sea-beaches and each of the three last-named resi- 

 duary effects of glacial action. 



With respect to scorings also and dressings on the surfaces of 

 rocks, it is very desirable that we should find some criterion where- 

 by to distinguish between the grinding eflfects of glaciers marching 

 slowly along dry land, and of icebergs dredging the bottom of the 

 sea, and of large stones and gravel drifted simply by water, in pro- 

 ducing striee, grooves and furrows, together with rounded and po- 

 lished surfaces on the rocks over which they respectively advance. 



I see not yet by what test we may distinguish these residuary 

 phsenomena where they occur in regions now remote from either of 

 the causes most competent to their production, viz. in countries that 

 now enjoy a temperate climate and are in some cases elevated nearly 

 four thousand feet above the level of the sea ; for where the sup- 

 posed agent is ice armed and transfixed with stones projecting like 

 the teeth of a file from its base and sides, the eff'ects of similar in- 

 struments on similar materials would probably be the same, by what- 

 ever cause a slow progressive motion may have been imparted to 

 them ; and whether on dry land or beneath the sea. 



It remains, moreover, to ascertain to what extent the sudden 

 elevations of land may have produced great movements of water 

 and diluvial inundations by gigantic waves, analogous to those 

 which are occasioned by modern submarine volcanic action ; and to 

 inquire into the effects that may have been produced on the sides 

 and bottoms of valleys of denudation by the drifting of the hard 

 materials that must have been swept through them at and after the 

 time of their excavation. 



A further subject of inquiry is, whether there be parallel strite and 

 furrows on the truncated and abraded surfaces of older rocks that 

 have been overlaid by more recent strata, after an interval in which 

 these surfaces had been exposed to the action of the sea. In cases 



