IDENTITY OF LIMESTONE BELTS. 435 



of the western pre-Mesozoic area, so closely allied in litbological char- 

 acter, position, sequence and character of fossils, were deposited under 

 indentical conditions, and are of the same age — Mesozoic. 



About a mile southwest of the line of limestone outcrops, along the 

 right side of the West branch of the Feather, in N. W. S section 19, T. 21 

 X., R. 4 E.. are two small exposures <A' limestone containing crinoidal frag- 

 ments. A short distance westward the metamorphic rocks pass beneath 

 Tertiary deposits, and consequently it is difficult to determine the exact 

 position of these limestones in the series. It is probable, however, that 

 a fault intervenes, and that these' are of the same horizon as those along 

 the right side of the West branch. 



Eastern principal Ana. — In the eastern principal area of Mesozoic ex- 

 posures the broad belt of serpentine, though varying in width and pos- 

 sibly interrupted in places, extends from the northern end of the range 

 to and across the Middle fork of American river. It therefore furnishes 

 convenient means of connecting the exposures of this area generally as 

 far south as to the last-named stream with those of the district already 

 described. 1 have followed it from this district southward to midway 

 between the Middle fork of the Feather and the North Yuba. It is 

 credibly reported as crossing the North Yuba between Downieville and 

 Goodyears bar, and this is confirmed by Professor W. IT. Pettee* Its 

 eastern edge crosses the South Yuba at the village of Washington, the 

 North fork of the American near Damascus, and the Middle fork of that 

 river west of Michigan bluffs. Its western edge crosses Hie last-named 

 stream in N. E. 1 section 1, T. 13 N., R. 10 E. Here, at its western edge, 

 ia a Large outcrop of pyritous talc. 



1 have not had opportunity to study the rocks next east of this ser- 

 pentine hell farther southward than midway between the Middle fork 

 of the American and the North Yuba. To that point the outcrops of 

 thinly laminated slate continue from the district already described on 

 the eastern side of the serpentine. From the South Yuba to the .Middle 

 fork of the American a broad area of the thinly laminated shales at the 

 head of the series adjoins the terpentine licit on the west. At one place 

 between the North and Middle forks of the American, where 1 have hail 

 opportunity to locate it roughly, the width is about •'! miles. 



Wes1 of the area of exposure of thinly laminated -late- again comes 



rpentine, with talcose rocks and slates, not in so widean area as on the 

 eastern side of the thinly laminated slates or so constant ; still, exposures 

 of serpentine with some talc are frequent, and they and the slates of the 

 same horizon I lower part of upper Mesozoic subgroup) are probably con- 

 stant from near Nevada city to the Middle fork of the American. How 



♦ Whitney's Vuriferoun (iruvels of the Sierra Nevaihi, 1870, : 



