4 B. Silliman on the Deep Placers of 
Corral, about 1500 feet, from whence it gradually rises into the 
high Sierras, the Yuba Gap Pass being 4570 feet above the sea, 
“ata —— Downieville Buttes about 8840 feet. This Mesopotamia 
hy 
summits of all the hills above a certain horizon, and in places 
reaches an elevation of from 2000 to 3000 feet above the level 
of the rivers. Below Columbia the denudation of the surface 
has removed the voleanic matter, leaving the auriferous gravel 
sembling pozzuolana or Roman cement. The accompanying sec- 
tion was made by Mr. Hugo Hochholzer to accompany his ma 
of = ridge, and represents the line drawn from the Fellows 
Quartz Lode, on the Middle Yuba, southeast through Snow Point 
and ‘Mount Zion, to the South Yuba. 
sé This section represents a point above most of the deep dig- 
gings, the gravel on this portion of the ridge beig generally 
covered by the volcanic cement, so as to be inaccessible by the 
process of hydraulic working, and available at a later day only 
by deep mining. 
_ It shows the ravines of the two branches of the Yuba at f 
Poo and g Gouth), the ‘bed rock’ a, the a us gravel 
the volcanic cement c covering all. The Siow Point 
Rae are eat at d, and the position of two of the water- 
ditches ate. 
gravel varies in thickness from 80 or 100 feet, 
where: it a ip exposed to denudation, to 250 feet or more, 
rs 
cst 
as 
Si i 
