378 
CONTRIBUTIONS TO ECONOMIC GEOLOGTY, 1902. [bull, zd 
ROCKS AT RIVERSIDE DAM SITE. 
Limestone (No. 3 in the following table) was obtained near River- 
side, on the road to the Pioneer mill, where it is found in large quan- 
tities along the roadside. The rhyolite (No. 4 in the following table) 
was found 2 miles south of the Riverside site. It offered the closest 
approach to a suitable silicate of alumina that could be found. 
The source of elements of silica and alumina in the crude materials 
should, however, be sedimentary in character, not igneous or meta- 
morphic. The analysis justified a trial mixture, and therefore one 
was calculated and made, but on burning the materials failed to 
effect the requisite combination for a Portland cement. Too large a 
percentage of the silica was in the free or uncombined condition. 
Fuel was not to be found near the Riverside site, and the manufac- 
ture of cement at this place is considered impracticable. 
ROCKS AT SAN CARLOS DAM SITE. 
The limestone from San Carlos site (No. 2 in the following table) 
was found to be admirably adapted to the purpose of the dam con- 
struction on account of its good specific gravity (which was 2.7), 
freedom from flaws, and siliceous character. It occurs in vast quan- 
tities, forming the abutments of the dam site. It forms bluffs, 
extending for several hundred feet, well located for quarrying. Large 
masses ma) 7 be embedded in the concrete, care being taken that they 
be laid irregularly in the mass of the dam, and are well placed so as 
to bond into a monolith. 
Analyses of rocks from I he vicinity of flic dam sites. 
[Chemical composition, in percentages. ] 
No. 
Name. 
Color. 
Locality. 
Sp. gr ; 
Car- 
bonate 
of lime, 
CaCO.j. 
Car- 
bonate 
of mag- 
nesia. 
Silica 
(SiOo). 
Alu- 
min-i 
and 
ferric 
oxide. 
Mois- 
ture. 
0.65 
1.00 
16.90 
Lime 
per 
cent in 
the 
car- 
bonate 
of lime. 
1 Limestone _ 
Gray... 
Pink . . . 
Blue.... 
White.. 
Pearl. 
Blue.... 
Gray . . _ 
96. 65 
55. 92 
93.10 
9. 60 
0.00 
31.00 
(UN) 
1.4 
3.7 
4.7 
60.9 
1.3 
6.0 
1.4 
12.6 
54. 124 
2 j do 
3 do... 
do 
Riverside 
2.7(1!! 
31.315 
52. 13(5 
4 
5 
Rhyolite 
do 
Limestone.. 
do ! 1.541 
Buttes i 2.3(51 
5. 376 
6 
90. 10 
55. 50 
0. 00 
0.00 
4.1 
34.6 
5.8 
7 do. 
do 
2.678 
1.3 
31.08 
From about U miles above dam site. 
The analysis of the gray or bluish limestone (No. 1 in the above 
table) shows from its freedom from magnesia and the small percent- 
age of free silica that it is possible to make a Portland cement with 
it, provided a suitable clay can be found to furnish the requisite 
elements of silica, alumina, and ferric oxide. 
