d+ THE AURIFEROUS GRAVELS OF THE SIERRA NEVADA. 
Survey, an unsolved problem. The highly metamorphic condition of a large 
portion of these rocks, the fact that the gold-bearing formations of the Ap- 
palachian chain, of the Ural and of Australia, had been proved to be of 
Paleozoic age, the repeatedly and strongly expressed dictum of an eminent 
authority, Sir Roderick Murchison, that gold could only be expected to be 
found in any considerable quantity in the oldest rocks, and the entire ab- 
sence of any fossil evidence throwmg light on the epoch of the auriferous 
belt of the Sierra Nevada,—all these facts combined had impressed geologists 
strongly with the belief that this formation could not be otherwise than of 
Paleozoic age.* The Silurian age of the gold-bearing rocks of the Pacific 
slope has indeed been attempted to be maintained by one of the geologists 
attached to the Pacific Railroad Survey, as late as 1866,+ and Murchison 
himself, in the fourth edition of Siluria, published in 1867, endeavors to 
throw doubt on the evidence collected by the California Survey, and set 
forth in detail in 1864 and 1865, in the first volumes of the Geology and 
Paleontology, showing the existence of Mesozoic fossils all along the line of 
the auriferous belt from Mariposa to Plumas County, and the absence of all 
proof of the Silurian or Devonian age of any portion of the rocks of that 
region. 
In view of these facts, it will be seen that it is quite desirable that the evi- 
dence with regard to the geological age of the auriferous belt of the Sierra 
Nevada should be passed in review. And it may be stated that, so far as 
* Murchison, in the third edition of his Siluria, published in 1859, — the year before the commence- 
ment of the California Survey — says (page 475), “ Whether, referring to ancient history, we cast our eyes to 
the countries watered by the Pactolus of Ovid, . . . . or to those chains in America and Australia which, 
previously unsearched, have proved so rich,—we invariably find the same constants in nature. In all 
these lands gold has been imparted abundantly to one class only of those ancient rocks [the Silurian], 
whose order and succession we have traced, or to the associated eruptive rocks.” Also (on page 455), “ We 
now know, therefore (and the recent explorations, in California, Oregon, etc., have confirmed the view), 
that sedimentary deposits of Silurian, Devonian, and Carboniferous age constitute the loftiest ranges and 
metalliferous plateaux of the American continent.” It is probable that Murchison found the desired con-- 
firmation of the views he had so long sedulously upheld in regard to the Silurian age of gold in Mr. W. 
P. Blake’s Report of a Geological Reconnaissance of California, published in 1858, — a reprint of part of 
his Pacific Railroad Report. He says (Introduction, page iv), “It is also probable that a great part of the 
rock formations of the Gold Region will ultimately be found to be Devonian and Silurian.” 
+ Bulletin de la Société Géologique de France (2), XXIII. 552. Séance du 7 Mai, 1866. 
t Murchison says in the fourth edition of Siluria, (page 471), “I can as yet see no valid reason to in- 
duce me to alter materially the generalization I adopted in my former edition, as derived from evidences 
in various parts of the world, viz. that the Silurian and associated Palaeozoic strata, together with the 
igneous rocks which penetrated them, have been the main recipients of gold.” The author, who thus 
