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University of California. 



|VOL. 3. 



terrace in sharp canons cut partly through the torrent fan, but 

 in one case not to its bottom. It is probable that much of the 

 slate debris was swept down from the slope without issuing 

 from these ravines. 



A single small remnant of^the original surface occurs near 

 the outer edge of the bed-rock platform. The bank displays 

 twenty feet of gravel, overlain by ten feet of reddish brown 

 sandy clay with small slate fragments. The surface is at least 

 120 feet above the river, but the terrace may have declined 

 another ten feet to the outer edge. 



Opposite the lower end of the Markusen Mine there was an 

 extensive remnant of the same terrace which has been mined 

 off to the extent of at least ten acres. The mine occupies a 

 point which projects beyond the center of the basin. It is 

 bordered on the riverward side by a precipitous black slate bluff 

 about ninety feet high. Portions of the rock platform, in the 

 form of shallow channels, may be only eighty feet above the 

 river. The high bank left at the inner edge shows at the base 

 about twelve feet of ordinary river gravel, overlain by a hori- 

 zontally stratified, reddish brown deposit, consisting of alternate 

 layers of sand and similar sand layers containing many small 

 well rounded slate pebbles. The thickness is about thirty feet. 

 Over it are fifty to seventy-five feet of non-stratified green 

 and red serpentine landslide debris, being the outer edge of the 

 great landslide belt mentioned in the paragraph describing the 

 Upper Basin. 



Farther out on the point the gravel was heavier, and twenty 

 feet or more deep, while the fine, gravelly material over it was 

 reduced to five feet. I cannot be certain that any portion of 

 the original surface is left here, but I am of the impression 

 that it formed a terrace about 110 feet above the fiver, going 

 back with a distinct slope until the presence of overlying land- 

 slide material gave it an undulating surface. On the bed-rock 

 floor there are some large, waterworn rock masses not strictly 

 local in origin, as the bed-rock is fissile black slate. Boulders 

 two or three feet in diameter were comparatively rare. 



This is undoubtedly a remnant of the same channel as the 

 upper channel of the Markusen Mine, and apparently also the 



