CONTACT OF THE TWO SUBGROUPS. • 427 



Here and southward granite forms the crest where not covered with 

 Tertiary materials, and the contact of these rocks and granite, passing 

 down the westerly slope of this part of' the eastern division of the range, 

 crosses the North fork of the Yuba about 4' miles east of Sierra city. 



On the other (southwesterly ) side of this northeastern belt of the lower 

 Mesozoic subgroup its rocks come in contact with those of the upper sub- 

 group. The contact crosses the East branch of the North fork of Feather 

 river, here known as Indian creek, a little northeast of ShooHy, near the 

 crossing of the line between townships 25 and 26 X.. K. ( .) E., then passes 

 on to the westerly slope of Hough mountain and of Grizzly ridge, and 

 crosses the Middle fork of Feather river between Bells bar and Nelson 

 point. 



In the upper part of this subgroup where it crosses the .Middle fork 

 of Feather river and thence a little east of southward to tin,' North fork 

 of the Yuba, one to two miles below Sierra city, are numerous outcrops 

 of limestone. For the most part they and the rocks accompanying them 

 are very much altered, ami I have seen no fossils in them. In sections 

 11 and 14. T. 21 X., R. 11 E., are several masses of iron ore which seems 

 to he a product of alteration of the limestone. Near the Yuba there is 

 some serpentine associated with the limestone. These limestones un- 

 doubtedly belong near the boundary of the two subgroups, at the same 

 horizon as the fossiliferous limestones to he hereafter described. Whether 

 the, outcrops of limestone recurring at intervals continue south of the 

 North Yuba 1 do not know. 



There is limestone exposed with a little serpentine in Little Long Val- 

 ley creek in section 12, T.£3 N.. R. HE. It is highly metamorphosed, and 

 1 do not know to what part of the lower subgroup it belongs. There is 

 a little serpentine near the crest of Grizzly ridge not far from its north- 

 westerly end. lint nowhere in this large eastern area of exposures of 

 the lower subgroup of Mesozoic rocks does serpentine occur in consider- 

 able mass. Near the crest of Grizzly ridge and near the divide between 

 the waters of the Middle fork of the Feather and of the North fork of the 

 Yuba and at (he Sierra buttes both slates and greenstones of this sub- 

 group are very generally altered to quartzites. 



( >n the easterly face of Spanish peak mountain there are isolated areas 

 of greenstones and slates of the Lower Mesozoic subgroup resting on the 

 pre-Mesozoic slates and quartzites. 



The rlareinont uplift has broughl pre-Mesozoic rocks in, contact with 

 mernbera of both Mesozoic subgroups, as shown on the sketch map. and 

 far northwestward of the present Claremont mountain the same uplifl 

 has dislocated the rocks and brought those of the two subgroups into 

 contact "lit of the regular order of sequence; so thai the rock- of the 



