XIV PREFACE. 



corded in this report, as well as a large i)art of the oxperfments. A jjortion . 

 of his time has been occupied in investigations which are not recorded here, 

 but which I iiope to publish soon. His work has been verj- difficult, but 

 entirely satisfactory to nie. 



Mr. H. W. Turner has assisted me in all the held work, and Chapter 

 XII is written from his notes. His accuracy and powers of observation have 

 been very valuable to me. Mr. Waldemar Lindgren joined me only in time 

 for the last season's field work. His assistance in the microscopical lithology 

 has been very efficient and important. I could not without aid have accom- 

 plished in a reasonable time so trying an investigation as that of the meta- 

 morphic rocks of the Coast Ranges. 



For myself, I may say that I have studied with care in the field 

 every portion of the areas surveyed in detail ; I spent months at the micro- 

 scope and nnxde many important chemical experiments on the solubility of 

 ores. It has been my endeavor to do justice to all sides of a very fine sub- 

 ject and to draw only legitimate conclusions from the facts observed by my 

 assistants and myself. I approached the problems mentioned above entirely 

 without preconceived ideas of the solutions to be reached, and have expressed 

 my conclusions as to the geology of California or of other regions without 

 regard to the opinions of others; but, while entertaining some confidence in 

 the correctness of my results for the region surveyed, I do not even incline 

 to the hypothesis that all crystalline sedimentary rocks have a history similar 

 to that of those which I have described or that ore deposits are all formed in 

 a similar way. 



The superintendents of the mines examined have afforded me every 

 facility, often at inconvenience to themselves, and I have much to thank 

 them for. Mr. Louis Janin has supplied me with many valuable notes 

 gathered in his large experience as a mining expert. Mr. Frank Reade, wht) 

 assisted me in examining the Conistock lode, was surveyor of the New 

 Almaden mine during the period covered by the present investigation, and 

 he prepared for me the excellent plans and sections of that mine. 



In addition to those who took part in the present investigation 1 am 

 indebted to numerous previous observers, to whom I have endeavored to 

 assign due credit in the proper places. 



