58 
GEOLOGICAL REPORT—THIRTY-FIFTH PARALLEL. 
Although there are many specimens of the granitic rocks in the collection, the material is 
not sufficient to authorize a comparison between the rocks of the different rauges. From some 
sections, especially the region of the Colorado and the Hawilhamook or Bill Williams’ fork, the 
specimens are quite numerous, and undoubtedly present a very fair view of the general mineral 
constitution of the ranges ; hut the representation from other localities is obviously not full and 
complete. As a description of each of the specimens will he found in a subsequent portion of 
this report, it is not necessary to repeat them here ; hut a few general observations will suffice. 
The most notable feature in the collection is the predominant red or rose-color of the speci¬ 
mens of granite, few or none of them being white or. light-grey. This reddish color is chiefly 
due to the pink feldspar, which is an almost constant ingredient. In several of the specimens 
a whitish feldspar or albite is mingled with the red, but the color of the latter predominates. 
The specimens contrast strongly with the collection which I made on the Siei’ra Nevada and 
the Bernardino Sierra, where the white albitic or grey granites and metamorphic rocks abound; 
but they much resemble the granites of the southern part of the Great Basin and those along 
the Mojave river. The absence of specimens of compact grey sienitic rocks is also worthy of 
note. But one specimen of distinct and well-characterized sienite is found in the series. This 
is No. 25, from the Colorado river below the Mojave villages. The hornblende in this specimen 
is the most conspicuous, and gives a greenish color to the mass. Another specimen, composed 
.of red feldspar and green hornblende, was found in the collection, but it was without a label. 
Two specimens labelled sienite were not found to contain any hornblende. 
The presence of metamorphic rocks at many places along the route is very clearly shown by 
the specimens. Their occurrence at other places is, however, mentioned in the descriptions ; 
and the collections must not be considered as a just representation of their position or mineral 
characters. Some of the most interesting localities, where the rocks are without much doubt 
metamorphic, may be enumerated as follows: At Little Rock schistose and slaty rocks crop out 
in nearly vertical strata, and are much contorted and traversed by quartz veins. The carbon¬ 
iferous strata rest horizontally upon their edges. In the Sandia mountains a compact green 
rock is found underlying the carboniferous limestone, which, from the specimen in the collection, 
I judge to be a metamorphosed clay slate. Mr. Marcou appears to regard these rock's next below 
the Carboniferous, as metamorphosed Devonian strata. The auriferous rocks of Gold mountain 
are in all probability metamorphic, but we as yet know little of their nature, the only informa¬ 
tion accessible being the statements of Lieutenant Abert and Dr. Wislizenus—the first that the 
ore occurs in limestone, and the second in sienite and greenstone. Gold is, however, now re¬ 
garded as a good indication of the Silurian age of the rocks in which it occurs, and it has been 
remarked “that it is a Silurian fossil.” It is not, however, confined to the metamorphic rocks of 
Silurian age, being certainly found in veins among erupted granitic and trappean rocks, and 
doubtless occurs whenever the mineral conditions of rocks are favorable, irrespective of their age. 
There is little doubt that the metamorphic rocks occur extensively in the Santa Fe mountains, 
for a wide ridge of slates breaking up into sharp angular pieces is mentioned by Lieutenant 
Abert as occurring between Taos and Santa Fe. 
Contorted gneiss occurs in the Aquarius mountains, the beds dipping to the west; and similar 
rocks occur on the opposite side of the stream in the Cerbat range. The presence of many veins 
of quartz and feldspar among the rocks of these mountains is also mentioned by Mr. Marcou. 
Iron ores were also found, and there are several varieties in the collection, but all of them are 
specular iron or the anhydrous sesquioxide. Metamorphic rocks were also found near the mouth 
of the river at its junction with the Great Colorado. It is most probable that a great part of 
the Pai-ute range is composed of metamorphic rocks. They occur without doubt along the 
Mojave, outcropping near the Spanish trail, in nearly vertical layers. They rise above the sur¬ 
face with a serrated outline, and rest upon a compact feldspathic granite, which is much fissured 
and traversed by feldspathic veins. A full description of these rocks has already been given. 
In the Bernardino Sierra the phenomena of metamorphism are well displayed, or rather the 
