976 THE JOURNAL OF GEOLOGY. 
Among the auriferous slates seven formations have been distin- 
guished, ranging in age from the Silurian to the Jurassic, inclusive. Of 
these the Cedar formation, of Triassic age, has been the most pro- 
ductive. By its disintegration it has furnished the gold for the placer 
mines of Indian Creek below Shoo Fly, of Soda Creek, Rush Creek, 
the north fork of Feather River, and Dutch Hill. The Savercool 
mine, by the north fork of Feather River, is on this belt, and active 
prospecting is going on at a number of points. Numerous copper 
deposits have been discovered in the Pit River region. 
Intermingled with the auriferous slates there are eruptive rocks, 
such as diabase, porphyrite, peridotite, and diorite, which have much 
to do in determining the distribution of certain classes of ore 
bodies. The areas of eruptive rocks have been outlined, and it has 
been found that the most promising prospects of that region are 
located near the borders of these eruptive masses. The ore deposits 
may be in the auriferous slates or the eruptive rock, but in either case 
they are not far from the contact. 
Traces of coal have been discovered in the Chico and lone forma- 
tions, but no deposits of considerable value are yet known in the region 
of Lassen Peak. ‘The Tuscan tuff has furnished some excellent mate- 
rial for chimneys, hearths, and water coolers. The large deposit of 
diatom earth on Pit River, having a thickness of over one hundred 
feet and a length of several miles, is of economic importance for pol- 
ishing, packing, making explosives, and other purposes. 
U.S. Geologic Atlas, Folio 17, Marysville, California, 1895. 
This folio consists of two pages of text descriptive of the Marys- 
ville tract, signed by Waldemar Lindgren and H. W. Turner, 
geologists, and G. F. Becker, geologist in charge; a topographic map 
(scale 1:125,000) of the tract, a sheet showing the areal geology, 
another showing the economic geology, and a third exhibiting 
structure sections. 
Topography.—The Marysville tract includes the territory between 
the meridians 121° 20’ and 122° and the parallels 39° and 39° 30’, 
and contains 925 square miles. ‘The tract is located near the center 
of the Sacramento Valley. The larger part of it is occupied by the 
alluvial plains of the Sacramento and Feather Rivers. The extreme 
northeastern corner includes the first rolling foothills of the Sierra 
Nevada. In the center of the tract rises the isolated mountain 
group of the Marysville Buttes. 
