DISTRIBUTION OF DRIFT ON THE SOUTH BRANCH. 255 



tively tranquil water of a shallow lake. The vast ac- 

 cumulations of sand and clay above them establish the 

 antiquity of the' arrangement, and the occurrence of two 

 such layers parallel to one another, and separated by 

 a considerable accumulation of clay and sand, leads to 

 the inference that the conditions which established the 

 existence of one layer also prevailed during the arrange- 

 ment of the other. These boulders may be distributed 

 over the level floor of a former lake or sea, and cover a 

 vast area ; if this be the case it only proves that the 

 agents which brought them operated a second time, after 

 a long intervening period, and with similar results. The 

 fine mud has been submitted to careful microscopical 

 investigation, without establishing the presence of dia- 

 tomaceas, or any organic forms from which conclusions 

 might be drawn respecting its origin. 



ERRATICS. 



The distribution of boulders or erratics in the area 

 explored, may be traced as in Canada to at least two 

 epochs ; the Drift and Boulder period, during which by 

 far the larger number were torn from the parent rock 

 and carried by ice to their present resting-places, and the 

 Eecent period,, including the rearrangement of ancient 

 drift and the distribution of fresh supplies by the 

 action of ice.* The largest boulder was seen in the 

 valley of the Qu'appelle. The circumference of this 

 enormous erratic is seventy-eight feet, and it exposes a 



* Where erratics are distributed in large quantities, the locality is indi- 

 cated on the map accompanying the Reports on the Assinniboine and Saskat- 

 chewan Exploring Expedition. 



