﻿1861.] 



HECTOR ROCKY MOUNTAINS, ETC. 



399 



which all point to a time when the rivers exercised a more powerful 

 influence than now ; as even small streams, such as Battle Biver, 

 flow through valleys from 150 to 250 feet deep, which have heen 

 partially refilled with stratified deposits. The sides of these valleys 

 are in general as regular and formal as those of a railway-cutting, 

 excepting where the nature of the strata causes frequent slides, or 

 harder beds give rise to a cliff- structure. The fiat alluvial bottoms 

 of these valleys are often four or five times the width of the river 

 which winds through them, and which is hemmed in by secondary 

 banks 30 to 40 feet high. The silt and alluvium are in general re- 

 gularly stratified, and almost every river-point contains one or more 

 lagoons, showing the frequent,, though slow, change in the river- 

 channeL 



Terrace-deposits of the Mountains. — At the distance of 90 miles 

 from the Bocky Mountains, the valleys of the rivers flowing to the 

 east commence to exhibit terraces composed of rounded fragments of 

 quartzite and limestone, such as woidd form the rounded shingle on 

 a rocky shore. At the Bocky Mountain House, where these terraces 

 first attracted my attention in the winter of 1857-58, the North 

 Saskatchewan has excavated a valley in the Cretaceous strata, which 

 varies greatly in its width, sometimes being hemmed in by perpen- 

 dicular cliffs of sandstone, and sometimes sloping gently back to the 

 elevated country on either hand where the strata had been less 

 able to resist the erosion. 



In this valley there are three terraces extensively developed at 20, 

 60, and 110 feet above the water-level*. Until we approach close 

 to the mountains these terrace-deposits are confined to the valleys 

 of the larger streams, but gradually they spread out, and at last cover 

 the whole country along the base of the mountains, filling up the 

 hollows and valleys of the outer ranges to the depth of several 

 hundred feet. This feature was observed at every point where we 

 approached the mountains from the east, from the 49th parallel north- 

 wards, and indeed was even better marked on the Athabasca Biver 

 than on any of those further south. Judging from the accounts of 

 American explorers, these terraces extend along the base of the Bocky 

 Mountains all the way south to Mexico. 



One hundred miles east of the mountains, in latitude 49° 30' 1ST., 

 shingle-beds are found to cap the Cypres Hills, which have an altitude 

 above the sea of 3800 feet, or nearly the same as that of the base of 

 the Bocky Mountains. The Cypres Hills are nothing more than the 

 western extremity of the great Missouri edteau, which, curiously 

 enough, here presents an escarpment to the west, and is separated from 

 the mountains by a tract of flat arid country of the above width. This 

 edteau is composed of Cretaceous and Tertiary strata, which have re- 

 mained as a dividing ridge, from the denudation having acted to the 

 north and south of the line which it marks. It is on the west and 

 south exposures of these hills that the shingle occurs, formed into 

 terraces like those along the mountains. 



These are not to be classed, however, with the river- terraces, which 

 * These are roughly introduced in fig, 7. p. 424. 



2 E 2 



