324 Tertiary. 



In the three prairie steppes there is a marked difference in the gen- 

 eral aspect of the surface of the country, and in the character of the 

 river valleys. On the first steppe, the surface is usually level, or un- 

 dulating in long gentle sweeps, and the beds of the principal streams 

 do not, probably, average more than 30 feet below the level of the sur- 

 rounding country. On the second steppe the surface is rolling, and 

 the river valleys are usually from 150 to 200 feet in depth, while on 

 the third, the hills are on a larger scale, and either closely crowded 

 together, or they rise here and there to considerable heights overlook- 

 ing less rugged tracts. The principal river-valleys on this steppe are 

 from 200 to 500 feet deep. The " coulees," as they are termed, form 

 a curious feature of the third prairie steppe. These are valleys, or 

 ravines, with steep sides, often one hundred feet or more in depth, which 

 terminate or close in, rather abruptl}^, often at both ends, forming a 

 long trough-like depression; or one of the extremities of the coulee 

 may open into the valley of a regular water-course. The coulees some- 

 times run for miles, and are either quite dry or hold ponds of bitter 

 water, which evaporate in the summer, and leave thin incrustations of 

 snow-white alkaline salts. 



The average depth of the river-valleys of the first and second prai- 

 rie steppes is not affected by the general descent of the country through 

 which they run. From the Little Boggy creek to the Arrow river, the 

 Assineboine must fall 400 or 500 feet, yet the banks of the valley 

 maintain the same general height and the same character throughout 

 the whole distance. Similarly, the fall in the Calling river, from the 

 Sand-Hills lake to its junction with the Assineboine, can pot be far 

 from 500 feet, and still its valley-banks have the same average height 

 throughout. The fall in the Red river, from Moorehead to Fort Garry, 

 is upward of 200 feet; but in the whole of the distance, the banks of 

 the river have a nearly uniform height of 20 to 30 feet. 



The great vallej's of the third steppe cut entirely through the drift 

 and far down into the uuderl3'ing Tertiary and Cretaceous rocks; those 

 of the second steppe appear to correspond, in a general way, with the 

 depth of the drift, while on the lowest steppe, the streams have merely 

 cut through the modified deposits resting upon the drift, which latter 

 is occasionally exposed at low water at the foot of the banks, or in the 

 bed of the stream at swift places and rapids. The stratified clay, silt, 

 sand, and gravel of the Red river and the lower Assineboine, vary in 

 thickness from almost nothing to 80 or 90 feet, and a variable thick- 

 ness of bowlder clay is interposed between these deposits and the older 



