-128 J. E. MILLS — LOCKS OF THE SIERRA NEVADA OF CALIFORNIA. 



lower subgroup which have the serpentines of the upper subgroup on 

 the southwest in the order of sequence, have slates of the same subgroup 

 on the northeast by fault. 



Fossiliferov.8 Limestones. — In the last named area of exposure of the 

 upper part of the lower Mesozoic subgroup occur the fossiliferous lime- 

 stones. The outcrops are not continuous, but occur at intervals from a 

 point on the southwestern flank of Claremont, in the N. E. \ N. E. I sec- 

 tion 4, T. 23 N., R. 9 E.,to and across Spanish creek and across the East 

 branch of the North fork of Feather river and the main North fork of 

 the same river to the divide between Mosquito and Yellow creeks, in the 

 western part of T. 26 N., R. 7 E., not far from the edge of the lava field 

 at the northern end of the range. The whole distance from the south- 

 eastern end to the northwestern end of this line of exposures is about 

 193 miles. From the southeasternmost exposure on Claremont to the 

 divide between the East branch of the North fork of the Feather and the 

 main North fork, a distance of 1-4 , miles, I have made detailed examina- 

 tion and surveys of the area, including the outcrops of these limestones 

 and of the rocks on either side. Thus examined and located, this long 

 line of outcrops of fossiliferous limestones in the heart of the Sierra afford 

 an' available and definite horizon from which to measure and determine 

 the position of rocks upward and downward in the series. 



Jurassic or later Age of th Fossils. — The fossil remains are fragmentary, 

 consisting principally of sections of crinoid stems, though fragments of 

 brachiopod and gasteropod shells occur. Some of the crinoidal stem- 

 joints are simple, round, and with round canal in the center; others, 

 however, are pentagonal and have pentapetalous figures formed bycren- 

 ated edges on the articulating facets. I sent some of these crinoidal 

 stem-joints to Dr. Charles Wachsmuth, whose extensive and intimate 

 knowledge of crinoids renders his identification of them most valuable. 

 In a letter concerning these fossils, dated at Burlington, Iowa, November 

 18,1891, he says: 



«* * * j examined them carefully and have come to the conclusion that they 

 must be at least of a later age than Triassic, possibly Jurassic. The stem-joints are 

 pentangular, with straight sides or reentering angles, and the facets in all of them 

 have that peculiar petaloid structure which characterizes the pentacrinidse, and 

 which occurs in no crinoid preceding the Jurassic. Scattered Let ween these stem- 

 joints there are numerous smaller pieces with a central canal, which I take to be 

 joints of the cirri, and of which in specimen 4 some are still attached to the edge 

 of the joint. On that specimen I also find a few perforated arm ossicles with deep 

 fossse, showing a highly developed articulation of the arms, such as is rarely found 

 in Paleozoic crinoids. The root on specimen 1 oilers no special interest; the lines 

 of union between the joints are serrated, but that is found even in some of the 

 earliest crinoids. That the stem is round at the distal end does not prove thai it 



