4:i4 



University of California. 



[Vol. 3. 



gravel, in which occurs a coarse, somewhat rough variety of 

 placer gold, quite unlike that usual to these deposits, and which 

 has evidently had a local source. Overlying this there is a bed 

 fifteen to twenty feet thick, consisting of very large, angular 

 rock masses, surrounded by a finely stratified brown fine gravel 

 and sand. Above this there is about thirty feet of debris, con- 

 sisting of a compact clay containing great quantities of rounded 

 and semi-rounded fragments largely of serpentine, and also 

 many large, angular rock masses. The color is greenish near the 

 base, but decidedly red near the top. There is no stratification. 

 From its general appearance I would at one time have pro- 

 nounced it a glacial deposit, but now I recognize it clearly as 

 the basal portion of an immense landslide. For a long distance 

 back of the mine the country has the peculiar landslide topog- 

 raphy. Where this landslide rests on the river deposit there 

 is a comparatively straight and sharp line. The formation of 

 the channel deposit immediately preceded the landslide. In 

 fact, the middle formation shows the desperate effort the river 

 made to dispose of the earlier landslide material. 



The Markusen Mine, situated on the north of the river, about 

 two miles above Orleans, has been operated mainly on one of 

 the finest remnants of the 120-foot terrace, of which about 

 fourteen acres have been mined off, leaving an expanse of boul- 

 der-strewn bed-rock about 1,500 feet long and 300 to 500 feet 

 wide. This consists of an irregular platform 90 to 100 feet 

 above the river, back of which there is a channel (the width of 

 which is not yet known) twenty to thirty feet deeper. Over the 

 bed-rock there was fifteen to twenty feet of moderately coarse 

 river gravel. Scattered about on the bed-rock there were a few 

 large boulders which remain intact and are the most remarkable 

 feature of this deposit. The bed-rock is black slate", but these 

 boulders are composed of a light yellowish or gray fine grained 

 material, apparently largely igneous, but containing abundant 

 inclusions of a hard laminated cherty rock, so that the term 

 breccia is properly applied to the boulders. I do not know 

 where this rock occurs in place, but I expect to find it up a 

 neighboring gulch along the line of the great thrust fault, as 

 somewhat similar breccia occurs along the fault toward the 

 south. 



