GREAT MOTHER LODE OF CALIFORNIA. 63 



the surface at intervals along regular lines, are familiarly known 

 to the miners as "gravestone slates." (Whitney, — Auriferous 

 Gravels, 44.) 



The principal slate belt begins a little to the south of 

 Mariposa Co. — it expands to a width of 20 miles or more soon 

 after entering it, and proceeds northward, with occasional inter- 

 ruptions, to the northern boundary of the State. This belt of slate 

 is known as the Grold Belt. Its surface is greatly diversified into 

 hills and valleys, and most of the valleys are filled, and many of 

 the lower hills are covered, with the gravel de^sosits which have 

 yielded such immense quantities of gold for the past 40 years, 

 and which have been evidently produced by its extensive denu- 

 dation. Near the northern boundary of Tuolumne Co., a lava 

 flow of late Tertiary age extends from the flank of the principal 

 range right across the gold belt, covering up and preserving the 

 auriferous gravels; and this is the first of a series of such flows, 

 which are met with in proceeding along the belt to the north- 

 ward. 



The slate belt was certainly metamorphosed before its 

 elevation, but whether it contained gold from its first origin is 

 still doubtful— if so, it was probably so evenly distributed through- 

 out the belt as to be of no economic impoi-tance. In the region 

 here in question, it varies from 10 to 30 miles in width, and it is 

 traversed for a great part of its length by what is known as the 

 "Mother Lode," or "Great Quartz "Vein,"— a great band of 

 quartzose dolomitic and magnesitic mineral, varying from a few 

 feet up to several hundreds of feet in width, and at least 80 

 miles long, which extends from the centre of Mariposa Co. 

 through Tuolumne and Calaveras to the centre of Amador Co., 

 parallel to the strike of the strata and to the general direction of 

 the main range of the Sierra Nevada. Beyond Amador Co. the 

 lode probably exists, but the gold belt is so much obscured with 

 overlying volcanic rocks, that the Mother Lode has not hitherto 

 been securely traced. Some authorities consider that it turns 

 somewhat abruptly northward through El Dorado and Placer- 

 ville, while others believe they have traced it on the Grass 

 Valley, and others again to Oroville. 



The Mother Lode is in many places, and especially in Mari- 

 posa Co., associated with serpentine and talc-slate, as well as 

 with argillaceous slate ; and it is specially important on account 



