LeConte and Rising — M<t>01if< -,>»"* Yr'm-fornuition, <t< 



THE attention of geologists has been already called by Mr. 

 Phillips* and Mr. Kollandf to the fact that, metalliferous veins 

 are even now forming at Steamboat Springs, in Nevada, and 

 at Sulphur Bank and other places in California; but the ob- 

 servations heretofore made at these places have been of a very 

 general character, and a mere careful examination seems still 

 a desideratum. Believing that any additional light, however 

 small, on so interesting a subject would be welcomed by chem- 

 ists and geologists, we have made repeated visits to Sulphur 

 Bank, viz: in 1877, 1878, 1879, 1880 and 1881, and spent 

 several days each time in examining the phenomena as they 

 occur there. In the meantime the mines which, during our 

 earlier visits, were mere open surface excavations, have been 

 recently developed in a systematic way. thus affording us op- 

 I'ortunities of. study which have not been enjoyed by any pre- 

 vious observers. The observations made on the ground have 

 been ever since the subject of continued thought, but the phe- 

 nomena are so complex that we desire this communication to 

 be considered only as a preliminary discussion. We hope, if 

 possible, to continue the investigation. 



Some genera] description of the Coast ranees and of the Sul- 

 phur Bank region will be necessary to make the subject clear. 



Coast ranges. — The Coast chain of California is a very com- 

 plex system of ranges with narrow valleys between, contrast- 

 rhe gram! -implieity of struc- 

 f the Sierra Nevada. The Cretaceous and 

 Tertiary strata of which it is composed are strongly folded into 

 repeated anticlines and synclines by the lateral pressure which 

 produced the ranges.}: As shown by the age of the newest 

 crumpled strata which enter into its composition, its birth-time 

 was the end of the Miocene. In some places the strata are 

 but in others they are intersected 

 by dikes and overflowed bv lava, and are therefore highly 

 metamorphic. This is especially true of the region to the 

 north of the Bav of San Francisco. The high moumain 



