OCR Text |
Show 89 north and the south, facing westward. To the west, a wide, elevated plain spread before ns, varied with a few hills, and stretching away with a gentle slope to Canon Largo and the country of the San Juan River. The discovery of the variegated marls was one of no little interest to the writer, inasmuch as I had made special efforts to find Eocene beds in this region, and trey were now crowned with success. The position of these marls, with their close physical resemblance to the Wahsatch beds of Bear River, Wyoming, together with the evidence furnished by a lower molar of Bathmodon, discovered by my guide, indicated that I had discovered the sediments of the great body of fresh water which during successive stages of the Eocene period occupied the drainage- basin of the Great Western Colorado. The thickness of the strata exhibited in the walls of the Cafioncita de las Vegas I estimated at 1,200 feet. On leaving the month of this canon, and proceeding southward, the southern dip of the red sandstones brings their summit to the ground- level in about ten miles distance, ( see Fig. 14.) The red and gray marls with alternating beds of white and yellowish sandstone appear on their summits, and at a point twenty miles south of the cafiou form a mass of bad- laud bluffs of from 600 to 1,000 feet elevation. This escarpment retreats aud then turns to. the east, forming an extensive horseshoe, the circumscribed area being occupied with bills and picturesque masses of sediment, with all the peculiar forms and desolation of bad- land scenery. I remained in camp for about a month near this circle, and obtained many fossil remains of Vertebrata.* Ten miles south of this point another horseshoe of bad lands covers an extensive area, and proved to be as rich in fossil remains as the first. Here I made my second camp, remaining in it for three weeks. The southern boundary of the northern tract exteuds to within six miles of the Cretaceous hog- backs, while the corresponding part of the second approaches nearer, forming a line of bluffs of considerable height running north and sonth parallel with, and half a mile from, the hog- backs. Beyond the Puerco divide, hills of this formation rise on both sides of the trail, and near the Qjo de San Jose", the Eocene beds repose on the foot of the Nacimiento Mountain several miles to the east. Below the sandstones which form the portals of the Cafioncita de las Vegas, another stratum of marls shows itself in hills of 100 feet and higher, iu the sage- brush plain that separatee them from the Cretaceous hog- backs. They are soft aud of mixed black and dark- green colors near the locality in question, and capped by light and yellowish sandstones. These are the lowest beds of the Eocene, and I traced them for forty miles to the south along the belt of country intervening between Cretaceous No. 4 and the reddish sandstone. At the locality just mentioned they conform to the sandstones above, having a dip of 10° southwest, while they do not conform to the hog- back of Cretaceous No. 3, the nearest available outcrop, which dips at 25° west. Farther south this marl is represented by low hills of generally lighter color. Near Nacimiento it has an increased, importance, as it rises both to the east and south. The valley of the Upper Puerco is excavated in it for some distance, and its blackish, greenish, and gray hills are seen on both sides of the river. At a point on the river about six miles below the village of Nacimiento, the lower sandstone of the Eocene forms a perpendicular bluff, which terminates in an escarpment of 500 feet elevation facing the south. The red- striped mail*, having acquired a gentle northern dip, disappear from view some miles to the north, and the termination of the underlying sandstones warned us that we were approaching the southern border of the basin. The border of the sandstone turned to the west at this point, the line of bluffs con-tinning as far as vision extended. Below and south of it the varied green and gray marls formed the material of the couutry, forming bad- land tracts of considerable extent and utter barrenness. They formed conical hills and flat meadows, intersected by deep arroyos, whose perpendicular walls constituted a great impediment to our progress. During the days of my examination of the region, heavy showers of rain fell, filling the arroyos with rushing torrents, and displaying a peculiar character of this marl when wet. It became slippery, reseuiblinc soap in consistence, so that the hills were climbed with difficulty, and on the levels the horses' feet sank at every step. The material is so easily transported that the drainage- channels are cut to a great depth, and the Puercp River becomes the receptacle of groat quantities of slimy- looking mnd. Its nnctuons appearance resembles strongly soft- soap, hence the name Ftierco, muddy. These soft marls cover a belt of some miles in width, and continue at the foot of another line of sandstone blutfo, whioh bound the immediate valley of the Puerco to a point eighteen miles below Nacimiento. Here the sandstone again turns to the westward, presenting asonthern escarpment of 500 to 1,000 feet elevation. This forms the southern boundary of the Eocene basin. I could not be sure whether this sandstone is identical with that of the escarpment twelve miles north, but suspected it to be such. Immediately south of it, low hills of Cretaceous No. 4 extend across the Puerco and continue south of the Eocene bluffs at a distauce of a mile or two with a * See Report on Fossil Vertebrata of New Mexico, An. Kept. Chief of Eugrs., 1874, and Systematic Catalogue of Vertebrata of the Eocene of New Mexico, 1875, 8vo, Geographical Explorations and Surveys West of the One hundredth Meridian, Lieut. G. M. Wheeler. LL- 7 |