SUPERFICIAL GEOLOGY OF BRITISH COLUMBIA. Ill 



gress. As a result of this action in the Fraser, the quartzite drift 

 developed in the vicinity of Fort George has been dragged down 

 stream in great quantity, and can still, I believe, be recognized as 

 an important constituent of the gravel banks to near tide-water. 



The display of terraces or "benches" on the Eraser and Thompson 

 rivers and some of their tributary streams is probably as imposing 

 as can be seen anywhere. In some cases they may show merely 

 stages in the descent of the rivers to their present levels through the 

 wide-spread deposits of the Glacial period ; but as many of them, 

 and especially those of the higher levels, are seen to leave the im- 

 mediate valleys of the rivers, attach themselves to the bases of the 

 hills, and fringe at similar elevations all the ramifications of the 

 streams into the plateau, it would seem that some at least must owe 

 their origin to the general inundation of the country, and its subse- 

 quent gradual drainage. Such an overflow may have been the result 

 of a general depression of the land, or of the stoppage of the southern 

 outlets, more especially of the Fraser valley, and, for the higher 

 terraces, those also of the streams running southward across the 

 49th parallel. Partial movements of upheaval and depression 

 might also account for the damming-back of water in valleys pre- 

 viously formed; but of this no evidence has yet been found*. 



In travelling up the Fraser valley through the Coast-range, one 

 has the widest opening anywhere existing through these mountains 

 at one's back ; yet, step by step, the terraces can be followed from 

 near the sea-level to the highest water-marks observed. At Yale, 

 on the outer border of the range, 160 feet above the sea, are ter- 

 races with narrow treads, composed chiefly of angular debris, but 

 forming well-marked horizontal lines on the mountain-slopes. One 

 of these, barometrically measured by my friend Mr. A. Bowman, 

 was found to have an elevation of 800 feet above Yale. The highest 

 perfectly distinct line was estimated to reach 1500 feet. It may be 

 open to question whether these benches may not be remnants of lateral 

 moraines of an old great glacier which has filled the valley. They 

 look, however, like shore-lines, caused by the accumulation and hori- 

 zontal arrangement below the water-line of debris from the moun- 

 tain-slopes. 



Following the gorge or canon of the river through the Coast-range, 

 besides lower terraces from 100 to 200 feet above the stream, every- 

 where visible, occasional fragments of benches bearing a close resem- 

 blance to those at Yale, may be seen perched far up on the mountain- 

 sides. About a mile above the Stoyoma river of the Admiralty Map 

 (25 miles above Yale) some of these were estimated to be as much 

 as 2000 feet above the water, or about 2450 feet above the sea. At 

 Boston Bar terraces estimated at about the same height were seen. 

 Near Lytton the Thompson river joins the Fraser, the valleys be- 

 come wider and the terraces well-defined and broad. One, baro- 



* Mr. Selwyn discusses some of these points in the Report of Progress Geol. 

 Surv. of Canada, 1871-72 (p. 55). Sir Matthew Begbie has also published 

 some account of the terraces of the Fraser ; but I have not been able to refer to 

 his paper. 



