02 MIZE, OWL INAIL (OIF (GIZ OLOGY, 
or less similar to that of the Robinson beds near Genesee Valley, 
but the rock in which the fossils occur is not itself a distinct tuff. 
It is composed of minute grains, probably of both quartz and 
feldspar, with abundant secondary greenish brown mica in minute 
irregular foils and green hornblende in slender fibers. The por- 
phyritic feldspars in the tuff (No. 219, Plumas county) found 
just north of the Little Grizzly Creek fossil beds, and with little 
doubt part of the same series, appear to be largely orthoclase. 
Another similar tuff from an area farther south (No. 352) con- 
tains likewise large feldspars, some of them three-tenths of an 
inch in diameter. These are in part microcline. The same greenish 
brown mica found at the two other localities above described is 
also present in the groundmass. This and the greenish horn- 
blende is probably the result of contact-metamorphism as granite 
occurs near each. A partial analysis by George Steiger, of No. 
352,shows it to have approximately the composition of a trachyte.* 
Following the Carboniferous comes the Trias. Beds of this age 
have been found at Mineral King, at Genesee Valley and on Rush 
Creek. At the latter locality is a bed of conglomerate inter- 
stratified with slate and limestone, the latter containing pentag- 
onal crinoid stems. This conglomerate was first discovered by 
J. E. Mills? and was visited by the writer in company with Mr. 
Diller. The pebbles of this conglomerate are well rounded, and 
may have been derived from land areas composed of Paleozoic 
rocks. Igneous pebbles are very abundant. These consist 
chiefly of quartz-diorites that seem originally to have been quartz- 
gabbros, the pyroxene now being hornblende. One pebble is 
chiefly made up of hornblende derived from pyroxene with a few 
spots of secondary material containing aggregates of minute, black 
particles, representing possibly original olivine, in which case 
this rock was a lherzolite. This pebble may have been derived 
from the large area now largely serpentine that forms Red Hill, 
just west of Rush Creek. Mr. Mills in his bulletin states that he 
found pebbles of granite like that forming Spanish Peak, but he 
* Fourteenth Annual Report, U. S. Geological Survey, p. 448. 
2 Bulletin Geological Society, Vol. IIL. p. 429. 
