THE "mother lode." 437 



edge of the Groat valley, culled Gopher hill, the eastern one Bear moun- 

 tain. The valley between the two is 3 to 4 miles wide. Along the axes 

 of uplift the exposures are principally if not wholly of the greenstones 

 and slates of the lower Mesozoic subgroup. Between the long narrow 

 belts of these exposures lie outcrops of the upper subgroup, and south of 

 the Calaveras, if not north of it, the serpentines and slates and the thin 

 slates of the upper subgroup occur again east of the easterly one of the 

 two axes of uplift, followed by the greenstones and slates of the lower 

 subgroup, which continue eastward to contact with pre-Mesozoic rocks. 



Large masses of limestone occur in this normal position in the series 

 at the head of the lower subgroup in places. The exposures of such 

 masses are especially frequent between the Calaveras and Mokelumne 

 and between the greenstones and lower slates brought up along the east- 

 erly one of the two axes of uplift on the east and the serpentines and 

 their accompanying slates on the west. I found a fossil coral at one of 

 the exposures at a Limestone quarry on the road from Campo Seco to 

 Mokelumne hill, a little less than 31 miles from the former in a straight 

 line, in the X. E. I S. E. 1 S. \V. ! section 23, T. 5 X., R. 11 E. 



A striking feature of this .Mesozoic area is the great gold-bearing quartz 

 lode called the " Mother lode." It occurs within the most easterly area 

 of exposure of the lower subgroup, the one lying next to contact with 

 the pre-Mesozoic rocks on the east. I have not had opportunity to de- 

 termine its exact position in the subgroup north of the Calaveras, but 

 between the Calaveras and Tuolumne it is. when present, at the head of 

 the lower or greenstone-bearing subgroup and at or near contact with 

 the serpentines and slated of the upper subgroup. At one place near 

 Carson Hill village it passes over the line between the two subgroups a 

 short distance and outcrops among serpentines and their accompanying 

 slates. 



Where the Tuolumne Hows out to the valley at Lagrange there are 

 greenstones of the lower subgroup and slates which are probably of the 

 upper subgroup. Where Merced river comes out of the mountains at 

 Merced falls the metamorphic rocks in contact with the Tertiary de- 

 posits of the valley are the thinly laminated slates at (be bead of the 



Mesozoic series. Farther southward, on the road from Merced falls to 

 I [ornitas, I -aw a small isolated patch of these slate- Lying on pre-Meso- 

 zoic rock-. 



Mesozoic Exposures south of th< Merced. — East of the pre-Mesozoic area 

 about Hornitas already briefly mentioned, and extending southeastward 

 from the Merced about L5 miles to where the pre-Mesozoic gneisses and 

 granites come forward to the valley, are two mountain-, already noted ; 

 the western is called Juniper ridge, and the eastern mount Bullion. The 



I.X I'.i o . i.i mi ~.„ , \ Mi . \ ,,, :, ism. 



