354 ASSINNIBOINE AND SASKATCHEWAN EXPEDITION. 



otherwise expended in warming the soil and advancing 

 vegetation. 



Lakes Winnipeg, Manitobah, and Winnipego-sis, to- 

 gether with the smaller lakes belonging to the Winnipeg 

 basin, are deeply frozen every winter ; ice often remains 

 in their northern extremities until the beginning of June 

 and greatly retards the progress of vegetation on their 

 immediate shores. The country is clothed with forests 

 giving rise to swamps where water accumulates. The 

 prairies are fully exposed to solar radiation and soon part 

 with their superabundant humidity. Hence one reason 

 that, north of the 47 th or 48th parallel, the mildness of 

 the seasons increases rapidly as we advance towards the 

 west, after leaving Eed Eiver. The improvement arises 

 not only from greater longitude, but is influenced by the 

 character of the rock formations by which the country is 

 underlaid and surrounded. The soil of the prairies is in 

 general dry and is rapidly warmed by the rays of the 

 sun in spring. The prairies enjoy too, north of the 58th 

 parallel, the genial, warm and comparatively humid winds 

 from the Pacific, which are felt as far north as the lati- 

 tude of Fort Simpson.* 



The mean annual temperature of 40°, as determined 

 by the Smithsonian Institution, passes through Canada 

 and Lake Superior, curves northward and leaves the 

 United States for British America at about the 103rd 

 meridian, crossing the South Branch of the Saskatchewan 

 north of the Elbow. 



The country embraced within the limits of our ex- 

 plorations may be divided into two regions in relation to 

 climate ; the arid and the humid region. The vast tree- 

 less prairie west of the Little Souris lies within that part 

 of the area which receives comparatively a small annual 



* Colonel Lefroy; Meteorological observations at Lake Athabasca and 

 Fort Simpson, p. 139. 



