GEOLOGY. 337 



and they run in every direction ; but usually their course coin- 

 cides with that of the mountain chain in which they are 

 found. The most remarkable vein of the State, and perhaps 

 of the world in extent, at least is the Mother Lode of the 

 Sierra Nevada. It has been traced for sixty miles, from the 

 Cosumnes River to Mariposa, in a southeast direction, with a 

 dip of about 45 to the northeast. The width varies greatly, 

 but the average may be thirty feet. The vein stone is a white 

 quartz, divided up into a multitude of seams, with gray and 

 brown discolorations, and with small proportions of iron, cop- 

 per, lead, antimony, and silver ores, besides gold, in the state 

 not of ore, but of metal. The Mother Lode is not only the 

 main support of a number of mining camps, but it also affects 

 the face of nature ; for such prominent elevations as Pefion 

 Blanco, Quartz Mountain, Carson Hill, a-nd Whisky Hill, seem 

 to be due entirely to the superior hardness of the large body 

 of quartz in this vein, which has defied the eroding powers, 

 while the softer slates adjacent have been washed away. The 

 hills stand in those places where the lode is widest and most 

 compact, and the rivers have sought out the intervening points 

 where the quartz was divided up into a multitude of little 

 seams, as at the crossings of the Mokelumne, Stanislaus, Tuol- 

 umne, and Merced Rivers, and Maxwell's Creek. 



264. Placers. The placers are alluvium that contains 

 gold. As the auriferous rocks were worn away, the lighter 

 and smaller particles were swept down into the level valleys, 

 while the larger pieces of stone and the materials of greater 

 specific gravity were left near the point where they were set 

 free. If a stream cut through a vein of auriferous quartz, 

 containing thick seams of gold, the largest lumps of the metal 

 would be near the point of intersection, the smaller lumps 

 would be carried down farther, and the fine scales might be 

 deposited many miles below. The smaller the pieces of gold, 

 as a general rule, the smoother they are, the smaller and 

 smoother the sand or gravel in which they are found, and the 

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