60 
GEOLOGICAL REPORT—THIRTY-FIFTH PARALLEL. 
probable that tbe eruptions of trap and porphyry which abound there have produced the 
result. Along the Mojave river horizontal tertiary strata are found resting in the basins of the 
granitic rocks ; and this is also the case in the Pai-ute mountains. 
The extensive outcrops of sandstone which we find at the summit of the Bernardino Sierra, 
at the Cajon Pass, have a modern aspect, but are without fossils. They are probably of Tertiary 
age, and are strongly upheaved. They may be regarded as evidence of granitic intrusions 
since their deposition, but it is by no means clear that the whole chain of granitic ridges has 
an origin so modern. We find tertiary strata resting undisturbed at the western and northern 
base of the chain, and it may be found that portions of the thick bank of horizontally stratified 
materials at the summit, and which form the upper edge of the long slope of the Mojave, are 
Tertiary. The uplifted sandstone which is found further west, and which is like that in the 
pass, also testifies to the violent dislocations and movements in that chain during or since the 
Tertiary era, provided it be proved that the sandstone is referable to this period. The localities 
of uplifted sandstone which have been referred to, are by no means the only ones which are 
found in that chain and near the point of its intersection with the Sierra Nevada. In the pass 
of San Francisquito, in Williamson’s Pass, and at the Canada de las Uvas, there are exten¬ 
sive outcrops, but some of them may be directly referred to the action of vast dykes of compact 
porphyry or greenstone. On the eastern side of the Sierra Nevada, at the Canada de las Uvas, 
there are disturbed sandstone strata containing fossil plants, which show their Tertiary or Post- 
Tertiary age. These strata are strongly upheaved and dislocated, and are found in the valleys 
of the granitic rocks of the chain ; but on the western base of the mountains there are extensive 
horizontal undisturbed deposites, 1,500 feet thick or more, from which great numbers of 
Miocene fossils were procured. This is not the only locality of Miocene fossils in undisturbed 
strata at the base of the Sierra Nevada. Mr. Marcou, however, states in his Resume, that the 
Sierra Nevada was raised at the end of either the Miocene or Pliocene periods, meaning the 
dislocation of strata of those periods, or upheaval of the chain, independent of the uplift of 
the “ Coast Range,” which he states was raised at the end of the Eocene epoch. 1 
In conclusion, it may be observed that much elaborate investigation is yet necessary before 
this subject of the relative ages of the numerous and extended mountain chains west of the 
Mississippi can be satisfactorily discussed. Tbe general conclusions to which we have arrived 
show, however, that chains which differ greatly in age are nearly coincident in direction, and 
that others which are probably synchronous, are diverging. The general northwest and south¬ 
east trend of the ranges west of the Rio Grande, and the more nearly east and west direction 
of the Bernardino Sierra, are worthy of note. Should it be proved that the Sierra Mogoyon 
is a continuous chain, its direction nearly conforms to that of the last mentioned chain. The 
parallelism and overlapping character of the ranges west of the Aztec mountains may be 
regarded as evidence of their stratified origin and subsequent plication. 
DEVONIAN. 
There is much reason to doubt whether the formations equivalent to those of the Devonian or 
Old Red Sandstone period are found along the line of the survey. They are mentioned by 
Mr. Marcou at only two points—at the Sandia mountains, and again at the western termination 
of the carboniferous rocks in the Aztec mountains. At the latter place there was probably the 
most reason to suspect its presence, but no fossils or other indication than the position of the 
strata beneath the carboniferous limestone served to identify them as the equivalent of the 
Devonian. In crossing the Albuquerque mountains—the Sandia range—the carboniferous 
limestone was found to be separated from contact with the granite by a mass of “serpentinoid 
trap containing strata of metamorphic limestone of Devonian age.” (Notes, October 5.) This 
serpentinoid trap, as will be seen by referring to the description of the collection, appears like 
1 See page 48 of Captain Whipple’s Report, in 8vo., Ho. Doc. 129, and in the reprint of the Resume' in the Appendix to 
this Report. 
