relation of ice oscillation to deposition. 369 



Oscillations of the Ice-margin. 



ft is abundantly clear that there have been several oscillations of the 

 ice-margin. Not only do the stratified seams and irregular, roughly 

 horizontal breaks in places in the upper portion of the bowlder-clay 

 show such advances and recessions of the ice, but the divergent courses 

 of stria' likewise denote several ice-movements as stated and indicate 

 that the bottom portion of the bowlder-clay lias Keen formed by a num- 

 ber of successive accretions or additions of material. The whole of the 

 bowlder-clay in question would seem, indeed, to have beni produced in 

 a zone of oscillation of the ice-front, the ice retiring to and advancing 

 from the Carleton and other hills to the north. The later advances were 

 comparatively light, otherwise the older or first-formed beds would have 

 been ploughed up much more deeply than they are. This may, however, 

 be partly due to the continued subsidence, which at the close of the 

 glacial or commencement of the Leda-clny period amounted to 220 feet 

 below the present high-tide level, in which case these deposits may 

 really have been thrown down in a sea of considerable depth. 



Climatic Conditions during Deposition of the Leda Clay and 



Sa xi cava Sands. 



The deposition of the Leda clay closely followed the last recession of 

 the ice and may, indeed, have been in progress before it finally disap- 

 peared from the bills around the mouth of the Saint John. The Leda- 

 clay fauna here does not denote such arctic conditions as prevailed in 

 the latter part of the glacial period, nor, indeed, in the Leda-cl&y period 

 in the gulf of Saint Lawrence. This has been shown by G. F. Matthew 

 and by Sir J. William Dawson.* The amelioration of climate following 

 the retreat of the ice was coincident with a rising of the land, as indi- 

 cated by the facies of the marine fauna found in the clays deposited in 

 the quieter bottoms and of that of the sands, etc, in the shallower sea 

 margins during the Leda-cl&y and Saxicava-s&nd period. No glacial 

 deposits are known to overlie these, or be inters tratified with them, on 

 the Atlantic coast of Canada. 



Conclusions. 



The conclusions drawn from the foregoing facts may therefore be thus 

 briefly summarized : 



1. The bowlder-clay here described was deposited at or near the margin 

 of the land ice which flowed out from the Saint John and Kennebeckasis 



*Notes on the post-Pliocene Mollusca of Acadia: G. F. Matthew, Canadian Naturalist, vol. vii 



Supplement to the 2d ed. of Acadian Geology, 1878. 



LV— Bum.. Gkol. Soc. Am,, Vol. 4, 1892. 



