Abundance of Gold.— Blake. 167 
either in a Cambro-Silurian series of slaty rocks and quartz or 
else has resulted from the immediate decomposition of those 
rocks. ”’ 
This last generalized statement would have passed unchal- 
lenged, and would have been generally accepted in the days of 
Sir Roderick Murchison, who came to regard the occurrence of 
gold as evidence of Silurian rocks, and conversely, the discovery 
of Silurian rocks, as for example in Australia, as indicative of 
the occurrence of gold, but to-day, after the experience in Cali- 
fornia, the generalization is not justified by the facts. 
The age of the chief gold-bearing slates of the central gold 
region of California, where gold was mined in greater quantity 
than ever before, was for a long time in doubt. The dogma of 
the Lower Paleozoic age of most of the gold rocks of the world, 
predisposed observers to regard the auriferous slates as Paleeozoic. 
But about the year 1864, T had the good fortune to find Mesozoic 
fossils in the midst of these slates, and thus removed all doubt 
of their true horizon. These fossils were Ammonites in the slates 
of Placer county near Colfax; Belemnites and Jurassic bivalves. 
in similar slates on the Mariposa estate, Mariposa county, and 
contiguous to the great gold quartz vein known as the Mother 
vein of California. Thus the Secondary age of the chief gold 
bearing slates of California was established. 
It is in this great belt of Jurasso-Triassic, and perhaps in part 
Lower Cretaceous strata, lying enfolded in the western flanks of 
the great mountain mass of the Sierra Nevada, we find the strongest, 
richest, and the most productive gold quartz mines and placer de- 
posits of California. The Mother vein at Carson hill, in Cala- 
veras county, has yielded some of the heaviest masses of gold 
ever taken from veins. Further,one of the deepest gold mines of 
the world is in the midst of the same great belt of Mesozoic slates. 
The occurrence of gold in California is, however, not confined 
to any one geological horizon. It is found in close contiguity to 
limestone of Carboniferous age, as early shown by Dr. Trask, and 
no doubt in the older rocks of the Sierra Nevada lying parallel 
with the chief auriferous deposits. Thus at Hite’s cove, some 
miles west of the locality of the Jura-Trias fossils of Mariposa, 
there is an important gold-bearing vein near a stratum of lime- 
stone in which I have found encrinal stems, and which is no 
doubt Upper Paleozoic. But these older strata in California have 
