Geological Notes on the Sierra Nevada, — Turner. 233 
liceous slate included in quartz-porphyry, which is the coun- 
try rock of the mine, and the ammonite presumably came 
from this slate lens. Mr. Stanton examined this locality for 
fossils, but found none. 
There are a number of lenses of precise^ similar black si- 
liceous slate in the quartz-porphyry, etc., that forms the crest 
of the ridge extending north from the Sierra buttes, and it is 
therefore probable that all of these rocks, both the lenses and 
the enclosing igneous rocks, are Jura-Trias in age. 
Apparently overlying the igneous rocks that contain the 
siliceous slate lenses area series of comparatively little altered 
sediments containing a large amount of fragmental diabasic 
material with some quartzite, fine-grained, reddish, clastic 
rocks, a variegated breccia and a few limestone lenses. The 
series is best exposed along and east of the north fork of the 
Yuba river, in the southeast corner of the Downieville sheet. 
in the neighborhood of the old stage station known as Milton, 
and the rocks are therefore provisionally called the Milton 
series. 
The breccia contains abundant small fragments of phthanite, ami 
other rocks of various colors. Pebbles of this breccia have been noted 
by the writer at a number of points in the Neocene auriferous gravels. 
Limestone was seen at two points only, both of the bodies being at the 
contact with the granite area to the east, and having yellow and red- 
dish garnets, presumably as a result of granitic contact metamorphism. 
The hardened sandstone or quartzite of the series contains a 
good deal of authigenetic brownish-green mica in minute foils, 
which may likewise be ascribed to metamorphism. There is. 
therefore, little doubt that the series is earlier in age than the granite 
mass to the east. This body of tuffs and sediments shows very little 
evidence, both macroscopically and microscopically, of having been 
greatly compressed. Not only, as a rule, has every little slaty structure 
been developed, but under the microscope t he augite and feldspar prisms 
and the quartz grains show little evidence of crushing. The series, as 
a whole, has a remarkably uniform dip of from 4.">° to 50° to the east. At 
the granite contact the dip is in places much steeper. It is probable thai 
these rocks are .Jura-Trias in age, although fossils have no1 been found 
in any portion of them. The series seems to rest unconformable on the 
presumably Paleozoic sediments that form the mass of the range on 
the Downieville sheet wesl Of Milton. These Paleozoic ( '.' ) rocks con- 
sist of black slates, quartzite and limestone, with intrusive quartz-por- 
phyry, gabbro, etc. They stand approximately vertical and are much 
compressed. The difference in the lithological characters of the two 
sets of rocks, the fact of one showing much evidence of dynamo-meta- 
