| OCR Text |
Show 281 interesting association of Cretaceous forms, consisting of numerous lnoeerami and Ostreee, besides Ammonites, Scaphites, Bnculites, and the fragmentary remains of fishes, representing at least two Teliostean genera and a Sqnaloid Qaleocerdo. In the plains east of the Canadian, similar and more extensive limestone deposits are known to occur, which are reported as containing the same faunal assemblage. Post- Tertiary.- From the base of the abrupt western boundary of the basin, the Cretaceous shales descend in gentle interrupted slopes far out into the valley, and which at one time must have formed a continuous shelving beach- like declivity along the flanking hills. But in the . process of the drainage of the basin and the consequent deepening of the channels of the numerous streams which come down from the mountains and neighboring table- lands, this sloping terrace was subjected to extensive erosion, until it now presents the condition of so many terrace* benches descending into the plain between the embouchures of the little valleys. They present all the phenomena of the Terrace epoch, notwithstanding they are wrought out of the Mesozoic deposits, and the mouths of the larger valleys are occupied by series of terraces in all respects resembling in form and position those which, in other parts of the country, are entirely made up of re- arranged drift materials. The terrace- benches which fill the mouth of the Cimarron Valley may be regarded as typical examples of these formations, in the molding of which the waters of the Cimarron have played an important part. Here there are at least four or five well- defined benches, ranging HI height above the present level of the stream from a few feet to 300 feet. The two highest of these benches, which now occupy the divide between the Cimarron and Cimarroncito, are, however, themselves, probably but remnants of the old lacustral beach which once extended continuously along the foot of the Tertiary plateau. The lower and by for the most extensive of these old benches attains an elevation of about 200 feet, forming a low mesa extending along the south side of the stream a distance of three miles. Its summit gradually slopes toward the plains, and, like the preceding, is clothed with a thin layer of coarse drift, the degradation of which has thickly strewn the declivities with small bowlders and pebbles, effectually concealing from view the Cretaceous shales upon which it rests. This mesa has been pierced by two or three lateral arroyas, besides the little valley which intervenes between its western extremity and the foot of the Tertiary- capped hills, in the sides of which natural sections of the fossiliferous Cretaceous shales are exposed at various points. The next distinct bench is that which occupies so considerable an area along the south side of the stream, and which drops to the level upon which the town is principally built, though it continues to follow the stream lower down, but much diminished in width. Above the town, this beneh reaches the height of 50 to 60 feet, and at a point where its base is washed by the stream an interesting section is exposed, showing the character of the superficial deposits which here deeply cover the terrace. The lower 30 feet or more of the exposure is made up of dark- blue shales of the Cretaceous period. Besting upon these occurs a heavy deposit of modified drift, the lower portion of which is apparently largely composed of sand with streaks of gravel; the upper six or seven feet exhibit a distiuct <! op" sit, made up of water- worn bowlders, pebbles, and gravel, which seeuis to immediately underlie the fine soil with which the terrace is mantled. Similar exhibitions of terra* formations, as before stated, are met with in the mouths of all the v « Vvs penetrating the great Tertiary plateau, and perhaps nowhere are more conspicuous and symmetrical |
