108 GEORGE MERCEK DAWSON ON THE 



July 22nd we camped on the north-east slope of the mountain, in the 

 valley of a little stream which, after running between high sloping 

 banks for about a quarter of a mile, opens widely north-eastward, 

 in which direction the whole surface at the same time slopes away. 

 Here distinct though somewhat worn terrace-marks occur in the 

 sides of the little valley ; and in travelling a short distance westward 

 along the mountain-side, there may be observed to spread quite be- 

 yond the valley of the brook, and form an extensive, nearly level or 

 only gently undulating, flat on its northern slope. The material of 

 the flat is evidently rolled and water-rounded, like beach-shingle, and, 

 though in great part derived from the volcanic rocks or the moun- 

 tain itself, has a considerable percentage of travelled stones, some of 

 which are as much as a foot in diameter. At higher levels on the 

 mountain-side this rounded material does not appear, and, as far as 

 observed, no fragments not referable to the rocks of the mountain 

 occur. Northward, with the possible exception of one peak forty 

 miles off, no land equal in height to this terrace is in sight. The 

 average elevation of the country is probably 2000 feet less. I have 

 not had the opportunity of examining other parts of this mountain 

 or the ranges east and west of it with care ; but from a distance the 

 south-east side of this one shows a well-marked line, separating the 

 higher peaks from the low sloping base. This was noted and sketched 

 as a marked feature before the existence of the shore-line above de- 

 scribed was known (fig. 5). In height the two must nearly if not 

 exactly agree ; and it is more than probable that the different appear- 

 ance of the lower and upper parts of the mountain is largely owing 

 to the distribution of the drift upon it. 



The general evidence of the submergence of the interior during the 

 formation of the Boulder-clay to an extent of from 4000 to 5000 feet, 

 depending on the composition and appearance of that deposit, has 

 already been given. The tendency of the Boulder-clay to form elevated 

 undulating plateaux, even when unsupported by the basaltic plateau 

 and resting on an uneven surface, has also been referred to. When 

 terraces occur in series upwards from river- or lake-valleys to the 

 summit of the plateau, the highest generally consist not of water- 

 washed sands and gravels, but of Boulder-clay, little or not at all 

 modified — a circumstance seeming to prove the formation of the 

 Boulder-clay to have been still in progress while the water passed 

 through the first stages of its retreat. In ascending from the Black- 

 water, these Boulder-clay terraces appear at about 3150 feet. 



The north-eastern or upper end of Tatlayoco Lake touches the 

 plateau-country, while its south-western stretches into the Coast 

 Mountains, through which its waters eventually pass to the sea. Its 

 elevation is 2747 feet ; and terraces quite well marked appear on its 

 south-eastern side to a height estimated at 1500 feet above its waters, 

 or 4250 feet above the sea. Fraser and Erangois Lakes are bor- 

 dered by terraces, the best-marked being estimated at 100 and 200 

 feet above the lakes respectively, which, allowing for their diffe- 

 rence in height, no doubt represent the same water-line, the approx- 

 imate elevation of which above the sea is 2350 feet. The hills 



