7 
~~. 
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, has 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- 
tigations 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: jirst, 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 1874. The most important 
portions of this work, by far, are the detailed explorations 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 has 
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 
