Jurassic Age from the Sierra JSevada. 279 



some distance over the slope although the identification is 

 made difficult by sliding rock masses and dense brush. In the 

 bottom of the canyon of the North Fork, however, the sedi- 

 mentary series is excellently exposed and here the conglomerate 

 may again be found, in particularly fresh condition. Along 

 the river the series mostly consists of dark sandstones and 

 slates ; the conglomerate is less developed than on the ridge 

 and the pebbles are somewhat smaller, but otherwise it is 

 identical with that from the former localities. Further east up 

 the river the before-mentioned breccias begin to appear in the 

 series. The conglomerate from the river is a very hard, dark- 

 colored rock composed of small but very smooth and round 

 pebbles (max. diam. l cm ) of gray, white or black phthanite, 

 gray limestone, black slate and white quartz, the latter being- 

 least abundant. The cement is black in color and very fine in 

 texture, apparently a consolidated mud. The conglomerate 

 from the summit of the ridge, somewhat softer from weather-, 

 ing, contains pebbles sometimes reaching 4 ' n in diam. ; the 

 quartz pebbles occur in variable quantities, occasionally very 

 abundant. Phthanite and limestone always make the bulk of 

 the pebbles. 



This conglomerate has not escaped the sharp eyes of the 

 prospectors of early clays and at three places at least shafts 

 have been sunk in it. Considering the rock identical with the 

 Tertiary, sometimes cemented, gravels found so abundantly 

 higher up on the ridge their object in sinking these shafts was 

 to attain the "bedrock" in the hope of there finding a paying 

 deposit. Their efforts were in vain and abandoned long ago. 

 One shaft south of the United States ranch was sunk 60' deep 

 about 40 years ago, also one of the shafts to the north of the 

 road. The attempt was renewed about 20 years ago and the 

 total depth attained in the north shaft about 80 feet. None 

 who had been connected with the work could be found and 

 conflicting reports were obtained as to whether any gold had 

 been found in the conglomerate. It is said that the gulches 

 in the vicinity had in early days yielded considerable gold in 

 well worn grains and particles ; the character of the gold 

 would indicate that it had come from the conglomerate. 



Numerous tests were made on specimens from three locali- 

 ties : first, rock extracted from the shaft south of the road ; 

 second, specimens from an outcrop about 300 feet west of that 

 shaft, and third, rock extracted from the deep shaft north of 

 the road on the ground belonging to the United States ranch. 

 In none of these specimens could any seams or veinlets of 

 quartz be seen, nor any indications noted that they had been 

 subjected to the influence of auriferous solutions. A few 

 pounds of each sample were repeatedly crushed in a clean 



