618 G. M. DAWSON ON THE SUPERFICIAL GEOLOGY OF 



drift is entirely composed of material derived from them, and con- 

 sists of quartzite, with softer shaly and slaty rocks, and limestone, 

 which is generally distinguishable from that of eastern origin. Wo 

 granitic or gneissic rocks occur in the vicinity of the forty-ninth 

 parallel, or northwards in British America, in the eastern ranges, so 

 far as is known. Southwards, in Montana, granites and gneisses are 

 found underlying all the other formations, but they do not appear to 

 be very extensively exposed. 



The Rocky Mountains. 



The brook issuing eastward from the mouth of the South Kootanie 

 Pass has cut through a great thickness of clean gravel drift, composed 

 of large and uniform well-rounded pebbles. Above the brook, on 

 the flanks of the mountains on the south side, are several well-pre- 

 served terrace-levels composed of similar material. The highest of 

 of these, though its altitude was not actually measured, was esti- 

 mated from the known altitude of the Pass to be about 4400 feet 

 above the sea. Prom the position of these terraces, in the open 

 eastern throat of the pass, from which the whole surface of the 

 country falls rapidly away, they can hardly be other than old sea- 

 marks. The topography of the region would not allow me to explain 

 them on any hypothesis of a former moraine blocking up the valley. 



Dr. Hector has measured similar terraces at several points along 

 the Rocky Mountains north of the region now more especially under 

 consideration, and states that they may be said to range from 3500 

 to 4500 feet above the sea. He also states that in the region ex- 

 amined by him the ordinary Laurentian erratics were not observed 

 above 3000 feet, but mentions a very remarkable line of boulders 

 of red granite deposited on the plains at a height of 3700 feet, which, 

 knowing what we now do of the country, can hardly be supposed 

 to have other origin than the Laurentian axis. It will be observed 

 that my measurements tally closely with Dr. Hector's for the more 

 northern part of the region. 



Among the Eocky Mountains themselves traces of .the former ac- 

 tion of glaciers are everywhere abundant, though in the part of the 

 range near the forty-ninth parallel glaciers do not at present exist. 

 The evidence here met with so closely resembles that found in many 

 other mountain-regions as to render it unnecessary that it should be 

 gone over in detail. Nearly all the valleys hold remnants of mo- 

 raines, some of them still very perfect. The harder rocks show the 

 usual rounded forms ; but striation was only observed in a single loca- 

 lity, and there coincided exactly with the main direction of the valley. 



The valleys radiating from the summits of greatest elevation 

 hold long lakes, many of which appear to be deep, and are filled 

 with the most pellucid water. "Whether they are in all cases dammed 

 in by moraine matter I was unable to determine. These longer 

 valleys very generally terminate in cirques, or amphitheatres, with 

 almost perpendicular back and, sides, which overlook small bat deep 

 terminal lakelets, held in by moraine-matter and shattered rock. 



