THE LA U RE NT! AN PENEPLAIN 629 



gradient of approximately a foot per mile. In a direction along 

 the divide (1,550') from southeast of Lake Mistassinni to Lake 

 Kaniapiskau (1,850') the rising gradient is almost exactly one 

 foot per mile. 



By way of comparison, from the profiles of the Canadian 

 Pacific Railway between Winnipeg (757') and Calgary (3,428') 

 in the foothills of the Rockies, the gradient is found to be 3.18 

 feet per mile. Between Edmonton (2,407') and East Selkirk 

 (744'), along the old location line, via the Yellowhead Pass, the 

 gradient is 2. i feet per mile. In each of the above cases, if shorter 

 sections are taken on each of the three prairie steps, it will be 

 found that for each step the gradient across the plains is much 

 less than the figures here given. ^ 



The comparison of the two gradients across the great plains 

 with the gradients upon the peneplain surface, taken in conjunction 

 with the character of the sky-lines in the two areas, shows the 

 appropriateness of the term "peneplain" as a term to describe 

 the principal geographic feature of this topographic unit. 



2. Departures from the 7iormal pe?ieplai?i type. — On an area 

 reduced to a peneplain one would expect to find a gently undulating 

 surface, with the larger streams meandering in broadly open 

 valleys. Their power to erode would long before have begun 

 gradually to diminish, in part by reason of the lessened rainfall 

 due to the reduced elevation above sea-level, in part because of 

 the reduced grade. Their sluggish character, diminished water- 

 supply, and low velocity will not enable them to transport the 

 waste of the land except in a very fine state of division, or in 

 solution. Hence the surface of a normal peneplain would be 

 composed of mantle rock of considerable depth, at the surface 

 very fine in texture, and gradually changing with depth to 

 unaltered bed rock. A very even surface, deep soils, and streams 

 which have long before lost the adjustments of earl}^ maturity, 

 the absence of lakes, and an elevation little above sea-level must 

 be characteristic features of a land area which has been reduced 



'In the profiles taken along the lines of river valleys it is to be noted that the 

 distances are estimated in straight lines, not along the stream courses. It will be 

 found that the average gradient of the stream course is much less. 



