390 ASSINNIBOINE AND SASKATCHEWAN EXPEDITION. 



In many places close to the water's edge and rising from 

 it in a slope for a space of twenty-five to thirty feet, the 

 fallen boulders are packed like stones in an artificial pave- 

 ment (g), and are often ground down to a uniform level 

 by the action of ice, exhibiting ice grooves and scratches 

 in the direction of the current. This pavement is visible 

 for many miles in aggregate length at the bends of the 

 river. Sometimes it resembles fine mosaic work, at other 

 times it is rugged, as where granite boulders have long 

 resisted the wear of the ice and protected those of softer 

 materials lying less exposed. 



Polished and Grooved Pavement of Boulders on the South Branch. 



Two tiers of boulders (c, /) separated by an interval of 

 twenty feet, are visible in the clay cliffs lower down the 

 river. When first noticed they (/) were about fifteen feet 

 above the water ; as we descended the stream they were 

 seen to rise above its level, preserving evidently a nearly 

 horizontal position. The lower tier (/) consists of very large 

 fragments of water-worn limestone, granite, and gneissoid 

 boulders; above them is an indurated sand containing 

 pebbles ; this is superimposed by an extremely fine stratified 

 clay (<?), breaking up into excessively thin layers, which 

 envelope detached particles of sand, small pebbles, and 

 aggregations of particles of sand. Above the fine stratified 

 clay, yellow clay and unstratified sand occur. The fine 

 clay must have been deposited in very quiet water, a 

 microscopic examination subsequently made, failed to re- 



