:>40 The American Geologist. April, 1894 
The [one claj pock or tuff is lighl in color, bul usually more or less 
discolored. The fracture is irregular as h rule, and it frequently con- 
tains minute tubular passages. Under the microscope it is seen to be 
composed of fine particles of feldspar and minute discolored fragments, 
-with some quartz grains. The [one (day rock is best developed west of 
Valley Springs. Analyses show silica contents varying from 52JE to V-.. 
and alkali contents varying from l.62jj to 4.s; ,. 
The lone sandstone plainly underlies the clay rock r as may be finely 
seen on the south hank of the Mokelumne river at the Camanche bridge. 
The sandstone is usually white in color, hut sometimes red. and occa- 
sionally passes over into a conglomerate with abundant quartz pebbles. 
It is quarried and used for building purposes, one of the red varieties 
bringing a good price in San Francisco. At the quarry from which this 
red rock comes, three miles southeast of Buena Vista in Amador county, 
the Pliocene shore gravels rest unconformably on the waterworn sur- 
face of the sandstone, here laid bare by the quarrying operations. 
Very characteristic of the lone sandstone is a hydrous silicate of 
aluminum, occurring largely as white pearly scales. The mineral under 
the microscope shows low polarization colors ami seems to extinguish 
parallel to the basal cleavage. The following analysis of the material 
was made by Dr. W. F. Hillebrand. who separated the foliated mineral 
from the quartz and other constituents by means of the heavy solution: 
Silica 55.88 Lime trace 
Potash 42 
Soda ::4 
Water below 100°C. .63 
Water above 100°C. 11.72 
Titanic acid 
.50 
Alumina 
.. 30.24 
Ferric oxide 
.42 
Ferrous oxide. . . . 
.Hi 
100.31 
The material analyzed showed under the microscope only a few par- 
ticles of quartz in the field of view. The foliated mineral comprised nil 
the remainder of the material. Perhaps K or 2% of silica mi.ffht be de- 
ducted as coming from these quartz grains. Prof. s. L. Penfield, to 
whom the material and thin sections were senl for examination, says 
that "as the aluminum silicate is not clear and transparent it is impos- 
ible to be sure that it does not contain microscopic quartz or chalcedony 
silica deposited on it.'" and is inclined to think the mineral an impure 
kaolinite. 
The while clay and sand beds are the lowest in the series and are 
best exposed about lone, where the coal seams they contain are mined. 
Al coal mine No. :>. borings to the depth of sc.o feel from the surface are 
reported in these clay ami sand beds. 
Mr. W. Lindgren found a series of beds of sandstone and clay with 
layers of lignite al the Marysville buttes, from which he obtained ma- 
rine fossil shells said by Dr. W. H. Dall to be of Miocene age. Mr. 
Lindgren considers these beds to belong t<> the lone formation. The 
series as a whole was undoubtedly, however, deposited in fresh OT brack- 
ish water. Search for fossils has been made at numerous points, but 
