14 The Ottawa Naturalist. [April 



face of the boulder clay, which covered the limestone outcrops, 

 the waters of the lake spread a thick coating of the finely- 

 ground shale that was excavated in the digging of the several 

 large valleys that cut through the plateau to the west. This 

 deposit, in lessening amount and thickness, is found over the 

 lake basin area north of the Red River Valley, and underlies 

 the plains around Dauphin, Swan and Red Deer lakes. 



On account of the soft nature of the rocks the stream 

 valleys are deeply incised, which adds to the difficulty of using 

 this passing water on the upland where it is often needed, since 

 the rainfall is barely sufficient during some seasons to make up 

 for the evaporation. Were these rivers nearer the surface the 

 question of diversion would be simple, but long and expensive 

 canals are required. The surface is generally treeless owing 

 to the light rainfall. Tree planting is proceeding rapidly 

 and is quite noticeable in Manitoba, where the bare prairie is 

 rapidly disappearing. This, if it does not induce a much 

 greater rainfall, retards the evaporation of the ground moisture. 



As a short summary, we may repeat that the basin which 

 received the muddy deposits of Cretaceous time has had a varied 

 history. The rocks of the western margin were elevated and 

 broken into long narrow blocks, which are piled up in succes- 

 sion to form the Rocky Mountains. A second strip was strongly 

 folded but not elevated as high as the mountains and con- 

 stitutes the foothills. A third strip formed a ridge in advance 

 of the folded foothills and now shows a simple synclinal struc- 

 ture, while the remainder, less disturbed but slo'oping generally 

 to the east, forms the Great Plains of the northwest provinces. 



SPRING ENCURSIONS, 1916. 



May 6 Rockcliffe to "McKay's Lak? and vicinity Geolo- 

 gical excursion. 



May 13 Cache Bay, west o~ Hull General Zoological 

 excursion. 



May 2 7 Ferry Lake and vicinity The study o c Botany 



to be given special attention. 

 June 10 Aylmer Park and vicinity General Zoological 



excursion. 



June 17 Experimental Farm Attention to be given 

 chiefly to practical Botany and Horticulture. 



