40 THE AURIFEROUS GRAVELS OF THE SIERRA NEVADA. 
a curious fact that proof of the existence of this peculiar and most interesting 
member of the geological series should only have been found in a single 
locality within the State of California, although it is distributed over so wide 
an area just beyond the borders of that State. 
At another locality in Plumas County, only a few miles from the one at 
which the Triassic fossils were found, a limited outcrop of a dark-red sand- 
stone was discovered, in 1863, which contained several recognizable species 
of fossils, among which Mr, Meek identified the following genera: Rhyncho- 
nella, Terebratula, Gryphewa, Pecten, Trigonia, Unicardium, Astarte, Myacites, and 
Belemnites. This is a grouping of genera not known to occur in rocks older 
than Jurassic, or newer than Cretaceous, while they are, as usually limited, 
common to both of these epochs. The weight of positive evidence, derived 
from the specific affinities of these fossils, as far as it goes, was declared by 
Mr. Meek to be on the side of the Jurassic, while the negative evidence de- 
ducible from the entire absence amongst them of any strictly Cretaceous 
types pointed in the same direction, and this conclusion was still further con- 
firmed by stratigraphical evidence, as already mentioned. Hence, Mr. Meek 
did not hesitate to describe the fossils in question as Jurassic.* We have, 
therefore, in close connection with each other two localities, in Plumas 
County, where rocks of undoubted Jurassic and Upper Triassic age occur. 
When we endeavor to connect these formations with those farther south in 
the gold-mining region proper, we get little or no assistance either from 
paleontological or stratigraphical considerations. The rocks of Plumas County 
cannot be correlated with those of Mariposa, and the paucity of fossils be- 
tween those two extreme ends of the auriferous belt renders it impossible to 
come to any more definite conclusions with regard to the geological age 
of the formation than those which have been mentioned in the preceding 
taining so exact a representation of the very peculiar Fauna of the Upper Trias of Europe, as exhibited in 
the St. Cassian, Aussee, and Hallstadt beds. For instance, there are, among the collections that have been 
found by different parties in these beds, the following peculiar genera, especially characteristic of the rocks 
of this age in Europe, viz. Halobia, Monotis, Cassianella, Trachyceras, Archestes, Clidonites, etc., directly 
associated with the more ancient genus Orthoceras. There have been also found in these beds the follow- 
ing species, closely allied to, or possibly in some cases identical with, Halobia Lommelet, Monotis Salinarzus, 
Ceratites Haidingerti, Archestes Ausseeanus, etc. There have also been found from this formation various 
other types of the Ammonitide, which, like those found at the same horizon in Europe, are not true Am- 
monites, nor Ceratites, nor yet Goniatites, as these genera have been restricted by late authors, but new 
generic types, sometimes intermediate in their characters between the typical forms of the above-men- 
tioned genera.” 
* See Palaeontology of California, Vol. I. 
