316 MINNESOTA BOTANICAL STUDIES 



As in the case of all recent moraines the soil consists of 

 boulders of all sizes up to occasional ones 10 m. in length. Inti- 

 mately mingled with these boulders is a large quantity of finer 

 material — small pebbles, sand, and very fine silt or "rock flour." 

 The accumulation of organic matter is very slight owing to the 

 recent origin of even the oldest parts of the moraines, and the 

 small amount of such material formed annually in a region of very 

 short and cool summers. In the newer parts of the moraine (all 

 regions less than 100 years old) the accumulation of humus is 

 entirely negligible. For similar reasons there has been but little 

 weathering of even the finer particles of the soil. 



Both moraines are watered by small streams which flow down 

 from the mountain sides and across the moraines, generally flowing 

 for a way obliquely or even longitudinally between parallel ridges 

 of the moraines. These streams have a constant flow, at least during 

 the warm season, being fed by melting snows upon the slopes above. 

 In point of moisture, therefore, the soil varies from the constantly 

 irrigated and sometimes even swampy margins of the streams, to 

 the tops of the ridges which are as dry as any soil can be in a 

 region where the snow lies until June, and a rainless week in summer 

 is less common than a week with seven rainy days. 



In all the above respects the north and south moraines are 

 essentially similar. In exposure they differ slightly, the general 

 slope of the south moraine being toward the northwest, the general 

 slope of the north moraine being toward the south. This difference 

 in exposure is really of little importance. There are numerous small 

 ridges with slopes in both directions, and the north moraine, which 

 as a whole gets the most direct sunshine at noon, is shaded by the 

 adjacent mountains during the early morning and late afternoon 

 hours. 



In chemical composition, however, the two moraines are en- 

 tirely different. The south moraine consists largely of fragments 

 brought down from Mt. Sir Sandford, and these are largely 

 crystalline limestone and dolomite. Mingled with these are frag- 

 ments of mica schist, and a little of a peculiar brown talcose schist 

 which occurs rather widely distributed throughout the Selkirks. 

 The north moraine consists of two portions. The upper, along the 

 side of the Silvertip glacier, is composed of granitic rocks from 

 the mountains at the head of that glacier, mingled with mica 

 schist from the nearer mountains. The lower part has received 



