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Show 167 more than 100 feet thick. This is real marble, and rune from north- northwest to south-southeast. All this canon is formed of gray granite exactly like the granite of the Sierra Madre and the Sierra Nevada, intersected here and there by dikes of milk- white quartz, dikes of rose- colored feldspath, and dikes of diorite. Sometimes, in place of the granite, we find gneiss and mica- schist, very much bent and twisted in all directions. Tertiary rocks in the vicinity of Fori Tejon.- At the outlet of the cafion into the plain of Tejon's ranch, we find Tertiary rocks composed of a heavy mass of clay, more or less saudy, with some thin strata of sandstone and limestone intercalated at different heights of the mass. The Tertiary rocks stand against the Sierra, and rise only to one-halt the height of the mountains which overlook the cafion. Some fossils are found in the sandstone, at the very entrance of the Canada de las Uvas; but, as these fossils are much more numerous aud in a better state of preservation three miles farther east, as one follows the foot of the mountains, at the Arroyo de los Alisos, ( Alder brook,) or Arroyo del Bancko Vieio, ( Old Ranch brook J I am going to give a detailed section, with a list of the fossils collected in this locality. The corral and the ruins of the Rancho de los Alisos are situated on the Quaternary drift, which is not very thick. Immediately afterward we come to hills of trachyte, trachy tic conglomerate, and| dolerite, which form the basis or first connter- fort of the mass of mountains. These eruptive rocks are the same as those of the Canada de las Uvas near Gorman's ranch. They seem to have raised the Tertiary strata very much. These latter dip to the south- southeast, toward the foot of the mountains, at an angle varying from 60c to 80° and 85°, almost perpendicularly at the spot where there is a fault in the bottom of the principal lateral ravine to the east of the arroyo. At the place where the section was taken, on the right bank of the arroyo, the eruptive rocks form four small ranges of hills, which gradually rise to a height of 350 feet above the plain of Tejon ranch. Immediately after passing the fourth hill, going up toward the mountain, we come to an abrupt bluff, which at first sight seems to be formed of drift. One soon sees, however, that the numerous rolled and much rounded pebbles that are met with are much flatter, and rocks whose composition are very differeut from that of those which constitute the ordinary Quaternary in the cations, and the cones of dejection of the cations of Tejon Pass, Las Tunas, La Pastorina, and Las Uvas. These rolled pebbles, moreover, are imbedded in a gray sandy clay of great hardness; finally, the whole is very much raised and dips in a south- southeasterly direction. This kiud of argillous conglomerate forms the basis of the Tertiary rocks of the region about Fort Tejon. Toward the top of the hill, instead of this conglomerate, we find gray clay, containing here and there intercalated strata of calcareo- arenaceous sandstone; some are entirely calcareous, while some other strata consist of pure sandstone. These calcareo-arenaceous strata vary from 1 foot to 2£ feet in thickness; they dip to the south, at an angle which is very much inclined, and which even reaches the perpendicular. At the bottom of the hill which separates the fifth hill or eminence rrotn the sixth, we find a well- defined fault; the strata of fossil iferous sandstone now dip to the north, at an angle of from 45° to 50°, and the beds on each side of the ravine do not correspond. Having reached the summit of the sixth hill, we see a small valley, with a gentle declivity, which lies at the point where the stratified Tertiary rocks form a junction with the granite and other crystalline rocks of the group of the Fort Tejon Mountains. These Tertiary rocks are, approximately, from 250 to 300 feet thick. All the strata of sandstone and arenaceous limestone contain fossils in greater or less abundance; some are even full of them, and form a real Lurnachdla ; thus, there are strata which might be called turrilitio beds, to such an extent do the liirrUites abound in them, reminding one of the ceritic limestone of the basin of Paris. In consequence of the hardness of the rock, it is difficult to obtain complete specimens of fossils; although they are in general well preserved, it is very difficult to collect anything more than fragments. Dr. Horn, the surgeon at Fort Tejon, has made a good and numerous collection of these fossils, which has been described by Mr. Gabb in the first two volqmse of the " Paleontology of California," published by that State. After having visited the locality explored by Dr. Horn, ai d having studied the geology of a portion of Southern California, I cannot adopt the opinion of Mr. Gabb, who considers this formation as cretaceous, and particularly resembling the Maastricht beds of Central Europe. I was not able to find a single cretaceous fossil, nor even any true cretaceous generic forms, in thin entire formation ; and I am altogether of the opinion expressed by Mr. Conrad, many years before Mr. Gabb, in volume 5 of Pacific Railroad Explorations, pages 318, 320, et 8* q. t who. judging from certain fossils found in an isolated block at the entrance of the Canada de las Uvas, has very judiciously referred these rocks to the Eocene- Tertiary formation. I go even further. I think that the rocks of the Arroyo del Rancho Viejo of Fort Tejon belong to the superior Eocene epoch, and that they are of about the age of the *' coarse limestone or caloaire grassier " of Paris. The fauna of Tejon reminds one very much of the fauna of the sands of Anvers, near Pontc; se, and of the sands of Gregnon, near Versailles. The following is a list of the |