34 G. M. DAWSON — GLACIAL DEPOSITS OF SOUTPIWESTERN ALBERTA. 



On the east the boundary of the foothills proper coincides with that 

 of the flexed strata, and is nearly ahvays quite definite, the corrugations 

 ceasing abruptly and being succeeded b}'' a wide, low S3''ncline, which is 

 continuous between the latitudes above referred to, and is occupied by 

 the remnants of a long elevated plateau — that of the Porcupine hills. 

 This plateau is throughout composed chiefly of sandstones of Upper 

 Laramie age, but the Porcupine hills proper extend only from Oldman 

 river northward to High wood river, a length of about 60 miles, with an 

 average width of some 20 miles. Further north they are represented by 

 a series of detached, lower plateau areas, which continue to border the 

 foothills on the east, while to the soutli of the Oldman the same syncline 

 is also occupied by plateaus, but still less prominent and lower. Of the 

 Porcupine hills proper, the highest part extends northward from the Old- 

 man for about 40 miles, and here a few points reach 5,300 to 5,400 or even 

 5,500 feet, while considerable areas of ridges and broken plateau exceed 

 4,500 feet. 



From the southern end of this high region, overlooking Oldman valley, 

 the view is open to the base of the Rocky mountains, no comparable 

 elevations of any extent existing in this part of the foothills. In the arc 

 from west to soutliwest the mountains are distinct from 20 to 25 miles, 

 but from the last bearing, around to south, the line of the mountains 

 recedes rapidly, being more than 40 miles distant where it crosses the 

 forty-ninth parallel. From south to southeast the lower continuing pla- 

 teaus alreadv mentioned are overlooked, but from southeast around to 

 north the outlook is across the sea-like expanse of the Great plains, of 

 which the rare, low, plateau-like elevations are scarcely distinguishable. 



A profile drawn across any part of the country above described would 

 show on the west the rugged front of the mountains (7,000 feet or more), 

 next the much lower l)ut irregular foothills, tlien a well marked depres- 

 sion separating these from tlie Porcupine hills, then the plateau of the 

 Porcupine hills, and lastly the long eastward or northeastward sIojdc of 

 the Great plains ; Init a profile traced along the valley of an}^ one of the 

 larger streams, and thus following the actual drainage level of the coun- 

 try, would show a nearly uniform descent from the base of the moun- 

 tains, only slightly increased in slo])e Avhile crossing the foothill belt. 

 These streams leave the mountains at an average elevation of about 4,350 

 feet. Along the eastern edge of the Porcupine syncline the plains have 

 a nearly uniform height of about 3,300 feet, with which the general level 

 of the rivers may be considered as practically coincident, although these 

 often occupy postglacial valleys of from 100 to 200 feet in depth below 

 the adjacent plain ; thence to the northeastward the surface of the plain 

 (with its rivers) gradually descends some 1,000 feet in a distance of about 

 120 miles. 



