78 
GEOLOGICAL REPORT—THIRTY FIFTH PARALLEL. 
Thus we find it in quantities in the Tertiary strata of Tuscany, where the large quantities of 
beautiful alabaster used for ornamental purposes are obtained. The vast deposites in the Andes 
of South America are associated with red sandstone and calcareous shales, and are believed to 
he in the lower cretaceous group. 
Grynsum is a common mineral in the soft and horizonal Tertiary strata of California, and is 
frequently found with red shales. It occurs at Ocoya creek in the Miocene, and along the 
entrance to the mountains from the desert in the red shales and sandstones of Carrizo creek, on 
the summit of which a thick bed of Miocene Tertiary fossils rests in a conformable position. 1 
It is thus seen that gypsum beds are by no means characteristic of the Triassic strata alone, 
hut that it is a widely diffused mineral, being found from the upper Tertiary down to the Lower 
Carboniferous. In fact we may expect to find it in any formation where the mineral conditions 
are favorable, and which have been subjected to decomposition and change either from the 
nature of the included minerals, or by the percolation of acid waters from above or below. The 
gypsum is by no means to he regarded as laid down at the time of the deposition of the strata? 
hut is a more modern formation, the result of decomposition and recomposition of the materials 
present in the strata, or supplied from without. 
We also find that the strata which the formation was thought to resemble, the gypseous strata 
of Windsor, Nova Scotia, and Plaister Cove, are not Triassic, but Carboniferous. This evidence, 
therefore, so far as it can be considered such, denotes a carboniferous age for the formation. 
The occurrence of salt and saliferous clays also appears to be regarded as evidence of the 
Triassic age of the formation. This mineral, like the gypsum, is found in many formations of 
different ages, being obtained in quantities in the Carboniferous and in the Cretaceous and Ter¬ 
tiary. Its occurrence is by no means to be regarded as evidence of the Triassic age of the 
strata. 
Another point of resemblance to the Triassic formation is found in the beds of dolomite or 
magnesian limestone; but at the point where this rock is best developed, according to the 
descriptions, along the Colorado Chiquito, it appears to be conformable with the carboniferous 
limestone, and is not separated from it by any great thickness of strata. In the absence of 
fossils, we cannot draw the line, and determine whether these magnesian limestones do not in 
fact belong to the Carboniferous. Their position favors this conclusion, the carboniferous lime¬ 
stone being the nearest rock identified by fossils. 
One of the strongest evidences of the presence of Triassic strata is found in the great thickness 
of the formation, if Mr. Marcou has not been misled regarding it. If the red gypseous strata 
attain a thickness of 6,000 feet, we may, with much reason, look for strata intermediate in age 
between the Carboniferous and the Cretaceous. But after a careful consideration of the whole 
matter, I am compelled to differ from the conclusion to which Mr. Marcou has arrived, and 
cannot regard the Triassic age of the formation as established. Triassic strata may be there, 
but their presence and their divisions are yet to be determined by fossils. 
The peculiar characteristics of the formation, as described, and its position relatively to 
the Carboniferous, suggest the possible Permian age of a portion, at least, of the strata. The 
resemblance of the lithological characters and position to the Permian deposites of Russia, as 
described by Sir R. J. Murchison, cannot fail to be noticed; and yet, being without fossils, we 
are not authorized to determine upon the age. We can only say, that the strata lie between 
known cretaceous beds above and carboniferous below. They may be in part cretaceous, as 
they most probably are—in part carboniferous, or may possibly contain representatives of all 
the Secondary group below the Cretaceous. 
■ I have already presented most of these facts, which show the distribution of gypsum in various formations and the 
impossibility of relying upon it as an evidence of the geological age of any series of strata, in the Report on the Geology of 
the route near the thirty-second parallel, explored by Brevet Captain Pope, U. S. Topographical Engineers. See 
Pacific Railroad Exploration and Surveys. 
