520 THE JOURNAL OF GEOLOGY. 



VI. Formations produced by winds acting on Pleistocene glacial 

 a?id glacio-fluvial deposits under the peculiar conditions of glaciation. 

 — It is not unreasonable to suppose that the tracts bordering the 

 great glaciers, especially those recently abandoned by them, 

 were exposed to very effective wind action. The differences of 

 temperature between the ice-clad fields and the adjacent ice-free 

 lands may be supposed to have induced strong wind currents. 

 Between their strength and the facilities offered for their action 

 by bare surfaces of recently-formed incoherent material, there is 

 ground for the belief that seolian deposits of more than usual 

 magnitude and of peculiar characteristics were formed. So also, 

 it is highly probable, if not certain, that some of the rivers of 

 glacial times were accompanied by broad flats which they had 

 themselves built up, and which they alternately flooded and left 

 exposed, and that here the winds found a special field of effective 

 action. Such seolian formations as resulted from these agencies 

 are probably not so important in themselves as in the erroneous 

 inferences to which they are likely to lead, if unrecognized. 

 Such wind-blown sands and silts might easily be borne up to 

 high levels and lodge there. If these are attributed to water 

 action (which seems the natural alternative) they lead to hypoth- 

 eses of flood-heights or of submersion of much magnitude ; and 

 these lead on to other conclusions of much consequence. The 

 recognition of the class, especially in framing working hypoth- 

 eses and interpretations, is thought to have some importance. 



With the foregoing general statements, we may turn to the 

 more special consideration of the several classes indicated. 



B. SUB-CLASSIFICATIONS. 



1 . Formations produced by the direct action of Pleistocene glaciers. 

 — Under this head may be recognized three sub-classes : 



i. Formations that gathered at the bottom of the glaciers. 



2. Formations derived from material borne on the glaciers 

 and within them (but not at their basal contact) and deposited 

 at their margins, or let directly down by their melting, when 

 stagnant. 



