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METAMORPHIC ROCKS—AGE OF THE CHAINS. 59 
effects are clearly visible. The rocks of the upper parts of the chain at the Cajon being very com- 
pact, and yet in most places showing lines of structure or lamination, while the debris of white 
limestone, traversed with blue bands or lines of stratification, not quite obliterated, show the 
former sedimentary origin of the whole. In the lower or southern part of the pass, slates are 
found similar to those of the pass of San Francisquito, further west, where gold has been ob- 
tained.! 
It is not possible, with our present limited information respecting these different localities of 
metamorphic rock, to form any conclusion with respect to their age. It is in all probability in 
most cases Silurian, or older than the Carboniferous. This is certainly true of all the localities 
east of the Aquarius mountains, for up to that point the carboniferous strata are present in a 
non-metamorphic state. The formations do not in any place appear to be like tue broad metamor- 
phic outcrops on the western base of the Sierra Nevada. They do not appear to consist of such 
vast masses of argillaceous and talcose slates, but are more compact, and gneissose. That the 
Azoic rocks occur is very probable, and the abundance of iron ores among Aquarius and Cerbat 
mountains would incline us to this opinion. Little value, however, can be attached to the indi- 
cations of age presented by the occurrence of the metals. The abrupt termination of the car- 
boniferous strata in horizontal strata at the Aztec mountains is not readily explained ; but it is 
most probable that beyond that point it has become metamorphosed, if, indeed, it ever existed. 
The limestone found in the Bernardino Sierra may be of this age. A limestone is also found in 
the Tejon Pass, in the Sierra Nevada, further west, and is there associated with beds of quartz 
rock or metamorphosed sandstone.? "The two localities are very probably similar in age. 
Relative ages of the several chains.— We may form some general conclusions with regard to 
the relative age of several of the granitic ranges, but cannot yet determine how recent many of 
the erupted granitic masses may be. "The horizontal carboniferous strata of the Aztec mount- 
ains at once point out the fact that we here have one of the most ancient granitic uplifts. The 
whole granite foundation, from the Aztec and Aquarius ranges eastward, probably as far as 
the Colorado Chiquito, is older than either the Sierra Nevada, Bernardino Sierra, or the ranges 
along the Rio Grande, the southern equivalent of the Rocky mountains. These granitic 
rocks of the Aztec mountains had received their form and position previous to the deposition of 
the carbeniferous limestone, while the Sierra Madre and Santa Fé mountains have been upraised 
since the carboniferous limestones and sandstones were deposited. We find the two latter 
ranges with the carboniferous strata flanking them, and dipping at angles of 30° and 35°. It ` 
was the opinion of Mr. Marcou that the Santa Fé mountains and Sierra Madre were later in 
origin than the beds of red clay and gypsum, and the overlying white sandstones, which he 
regarded as Triassic and Jurassic, and it was his belief that these formations were uplifted by 
the intrusion of the two ranges. We have, however, seen that the strata of the gypsum forma- 
tion and the Cretaceous are not disturbed to any great extent, but rest horizontally in the valley 
between the two ranges. Further observations on this subject are presented with the general 
observations on these two formations. 
itchita Mountains.—The carboniferous strata in the vicinity of the Witchita mountains, and 
along the line of granitic outcrops, extending east, or a few degrees north of east from them, 
. are more or less uplifted and disturbed, as if the granite ridges had been upraised since their 
deposition. This line of dislocation would thus appear to be near the age of that of the Santa 
Fé mountains. The metamorphic schists of Little Rock are, however, capped by the horizontal 
beds of carboniferous sandstone, showing the uplift of that portion at least to be anterior. ` 
Ranges along the Colorado.—It is not possible to determine the relative ages of these eegen 
Mr. Marcou records the presence of thick strata of tertiary rocks, upheaved and metamorphosed ; 
but it is not certain that their disturbance was produced by granitic movements. It is more 
1 For a description of these rocks see the author's Geological Report on the route surveyed in California by pore RT 
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