-" 



. . 



PREFACE. 



IX 



The necessity of making the above specified computations, as well as the large size 

 of the work and the number of illustrations which it required, has caused the pub- 

 lication of this volume to extend itself over a much longer period than was at first 

 expected. A portion of the delay, however, lias been caused by the time required for 

 making additional explorations in the field ; for, in view of the fact that the original 

 material had become somewhat antiquated, it seemed very desirable that further inves- 

 tioations should be made in the gravel region, especially in the northern portion of it, 

 where our work had never been carried on in a detailed manner. For this purpose 

 I was fortunate in being able to secure the services of Professor Pettee, previously 

 employed in similar work on the California Survey, and the results of his re-examination 

 of certain districts previously investigated by himself and others, as well as of further 

 explorations in more northern counties, will be found in Appendix A. These results 

 were received and examined by me previous to the writing of Chapter IV, in which 

 the theory of the gravels is discussed with some detail, although not as fully as I 

 could have wished had space permitted. 



As at present put together, the volume includes the following materials : first, the 

 investigations of the Geological Survey in the gravel region, carried on at various 

 times during its progress up to the time of its stoppage in L 1874. The most important 

 portions of this work, by far, are the detailed exploration^- of Messrs. Goodyear and 

 Pettee in the fields noted in the body of the volume as having been assigned to them. 

 Their explorations were supplemented by my own observations, which extended over 

 the whole gravel region from Mariposa to Plumas, although necessarily not especially 

 detailed in any one district. Second, the re-examination of certain districts and addi- 

 tional investigations of others made by Professor Pettee in 1879, as mentioned above. 

 Third, the barometrical observations for altitude made in the gravel region at various 

 times, by different observers, but chiefly by Messrs. Goodyear and Pettee. These have 

 been carefully recomputed by Professor Pettee, since the publication of the " Barometric 

 Hypsometry," with the use of the tables prepared for California, as already stated. 



The fossil plants of the auriferous gravels have been investigated by Mr. Lesquereux, 

 and his results, illustrated by ten double plates, properly form a supplement to the 

 present work. It did not appear necessary that any separate memoir should be prepared 

 in relation to the vertebrate remains, not human, of the gravels, as these had already 

 been worked up by Dr. Leidy, and published in connection with his descriptions of 

 other materials of a similar nature, from regions of the Cordilleras farther east and more 

 prolific in vertebrate fossils. The scantiness of our collections in this department lias 

 been alluded to and explained in the body of the present volume. 



There will undoubtedly be much hesitancy on the part of anthropologists and others, 

 in accepting the results regarding the Tertiary age of man to which our investigations 

 in the gravels of the Sierra Nevada seem so clearly to point. I feel, however, very 

 strongly, that I should not have been justified in withholding such facts as came to 

 my knowledge, and which seem to be perfectly well authenticated, merely because they 





