108 GEOLOGICAL REPORT—THIRTY-FIFTH PARALLEL. 
readily in one direction than in another. It is composed of a succession of layers of hornblende 
and mica with white quartz and feldspar. 
Nos. 21 and 22. Bill Williams’ fork.—This specimen is peculiar in its appearance, and con- 
sists chiefly of irregular masses and fragments of white granular quartz, imbedded in a greenish 
paste or matrix. One of the specimens contains small, partly decomposed cubes of iron pyrites. 
No. 23. Camp near Picacho.—A rose-colored granite, containing grains of feldspar of two 
colors. The mica is light-colored and silvery, and in distinct plates. The texture of the 
specimen is not even. 
No. 24. Between the Colorado and the Mojave rivers.—A hard, compact, even-grained, and 
dark-colored granite. In this rock the feldspar has a slightly reddish color, and is well crys- 
tallized; it is very evenly distributed among the other minerals, which are present in nearly 
equal quantities. The mica is dark, and in distinct crystalline grains. This rock, if abundant, 
would make beautiful building-stone. 
No. 25. Rio Colorado, below the Mojave villages.—'This specimen is a well-characterized sie- 
nite, consisting of feldspar and hornblende—the former in very irregular, amorphous, or granu- 
lar masses; and the latter well crystallized, and showing the characteristic cleavage of the 
species on all parts of the specimen. It has a green color, which is also the predominating 
color of the specimen, it being modified by the grains of white feldspar only. No quartz or 
mica can be seen in this rock. It is probably erupted, and not metamorphic. 
No. 26. Colorado river, below the Mojave villages.—This specimen consists of white quartz 
and feldspar in alternate layers, interleaved with films of mica, thus showing a structural char- 
acter, and indicating a sedimentary origin, and that it is metamorphic. 
No. 27. Cajon creek.—A beautiful white, crystalline limestone. This rock is perfectly white, 
and has a beautiful crystalline grain, which renders the fractured surfaces very brilliant. It is 
a beautiful marble, and is well suited for buildings. The specimen being labelled Cajon creek, 
leads me to conclude that it was broken from a rolled or transported fragment, especially as I 
myself saw blocks of this limestone in the bed of that creek, but was not able to find the source 
or outcrop from which they were broken. It probably exists in the high ridges on the east of 
the valley of the pass. 
No. 30. Camp 52.—This specimen is labelled ‘‘ Sulfate de Baryte,’’ but probably by mistake, 
since it consists of white feldspar, with its characteristic cleavage. It contains several small 
masses of translucent quartz, and is from a coarse granite or a granite vein. 
No. 31. Between Tuerto and Galisteo.—Mr. Marcou has labelled this specimen ** Hornblende 
rock," which it may very properly be called, consisting, as it does, chiefly of black hornblende 
in small crystals, intermingled with white granules of feldspar and quartz, giving the whole 
mass a dark grey color. The hornblende appears to be disposed in parallel planes, and a 
Structure is thus given to the rock, and it might be called a hornblende slate. 
No. 36. Near to Picacho.—This specimen is a reddish and granular granite, of very fine 
grain, so that it at first resembles sandstone. The feldspar is red, and one or two small, well- 
formed crystals, of a more glassy and colorless variety, are seen in the specimen. The mica is 
in small, brilliant scales, and is abundantly disseminated. 
No. 37. Pueblo creek.—This specimen is an amorphous, compact mass of reddish rock, proba- 
bly feldspathic. 1t is marked metamorphic by Mr. Marcou, but it is impossible to determine 
to what formation it belonged, nor are its characters sufficiently well marked to determine its 
mineral character without analysis, 
VOLCANIC ROCKS. 
[No. 38 to No 59.] 
No. 38. Trap forming a dyke in the White Chalk, Rio Galisteo, New Mexico.—This specimen 
presents weathered surfaces on all sides but one, and appears to have been broken from @ loose 
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