82 GEOLOGICAL REPORT—THIRTY FIFTH PARALLEL. 
of a rock by its lithological characters, the resemblance cannot be regarded as good evidence of 
their Tertiary age. The mineral characters are, nevertheless, of great importance as an indi- 
cation of the age, and it is presumed that Mr. Marcou was chiefly guided by them in assigning 
the age to the sandstone strata found on the route at and beyond Cactus Pass. 
We do not find in the notes made by Mr. Marcou any reference to Tertiary formations along 
the route until after the expedition had passed beyond San Francisco volcano. The Post Ter. 
tiary or Quaternary deposites are of course excepted—frequent mention of them being made. 
It would appear from the observations of Mr. Featherstonhaugh that Tertiary strata are 
developed at Little Rock and in its vicinity. He cites the occurrence of fossils of the genera Os- 
trea, Turritella, Calyptrea, and Cerithium, in a calcareous matrix on the south bank of the river. 
The same deposite is said to occur a few miles further west, where it is so calcareous that it was 
used to make lime.! This is the only record I can find respecting Tertiary deposites at that 
point. If Mr. Featherstonhaugh is correct in referring this deposite to the Tertiary, it is 
doubtless the fact that extensive areas of the surface and portions of the bottoms of the extended 
valleys or depressions in the carboniferous strata in that region are covered by strata of this 
formation. 
The strata of brecciated sandstone and calcareous conglomerate found outcropping near Camps 
16, 17, 18, and 19, are very probably Tertiary, but no fossils were found. 
There is much reason to believe that the cretaceous strata of the Llano are surmounted by 
Tertiary deposites over a part of the plain. This is indicated by the second line of bluffs, or 
second step, seen from the valley of the Canadian. Dr. Shumard also, who examined the Llano 
at the sources of the Red river, found a layer of rounded gravel and pebbles upon the top, which 
he denominates drift, and which at some places was found to be about 100 feet thick. Frag- 
ments of agate and carnelian, and of silicified wood, appear to abound in this deposite. The 
same pebbly bed appears to be found west of the Sierra Madre on the table-lands of Zuñi and its 
vicinity. These are, in all probability, Tertiary or Post Tertiary deposites ; but as they are not 
characterized by fossils, and as their extent is not known, I have not indicated them on the map. 
In ascending Cactus Pass, strata of sand and a coarse limestone were found outcropping in 
connexion with dykes of trap and porphyry. The strata inclined strongly towards the west, 
the trend being north and south. These are said to be Tertiary by Mr. Marcou. (Notes, Janu- 
ary 31.) "Tertiary deposites, according to the notes, were again met along the valley of Hawil- 
hamook, near Camp 121. At that place intrusions of trap rock have raised up strata of sand- 
stone and conglomerate of a red color. They were very friable, and have a reddish-yellow color, 
differing from the color of the older red sandstone. (Notes, February 13.) Similar strata were 
observed between Camps 122 and 123, and again between Camps 125 and 126. This formation 
appears to have extended along the valley of the stream down to the Colorado. It was again 
found along the Colorado, and between Camps 127 and 128 the strata were uplifted at an angle 
of 20°. The mountains which border the river beyond Camp 128 are composed of Tertiary red 
sandstones and conglomerates, metamorphosed and traversed by basaltic trap and amygdaloid. 
(Notes, February 22.) This red sandstone and conglomerate was afterwards found associated 
with white and chalky clay. 
Beyond the Colorado, towards the Mojave river, metamorphic conglomerate was found in 
ascending the mountains. (Notes, March 2d and 3d.) A whitish limestone, brecciated and in 
horizontal strata, was found on the 4th, between Camps 137 and 138. This was at an elevation 
of about 4,500 feet. 
Horizontal strata of white and bluish clay and grey sandstone, very friable, are found along 
the Mojave river in high banks near the point where the Mormon road leaves the stream to 
ascend to the Cajon Pass. Similar strata, but more deeply eroded, are found lower down the 
stream. "They are doubtless Tertiary. 
1 Featherstonhaugh's Report, p. 60. 
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