OCR Text |
Show 280 latter, the Canadiau glides into its great caiion, and thence, far to the south, its channel is said to be walled in by precipitous bluffs of red and variegated sandstone. At the entrance to the canon, the lowest point in the basin, the stream has an altitude of about 5,700 feet above tide- water. In the distance of forty- five miles direct, or to the confluence of the Eio Mora, the stream has a descent of probably 700 feet, along a part of its course but little known, and, it is believed, as yet unexplored by the geologist. Above the canon, the stream traverses a broad valley, which gradually slopes from the base of the Tertiary plateau on the west; its eastern border being less uninterruptedly defined by the confused range of volcanic hills and basalt- capped mesas, which rest upon and pierce the sedimentary formations south and east of the Chicories Mesa, a shallow, triangularly- shaped basin, with an area of about nine hundred square miles, its sharp angle terminating near the southern foot of the Raton Pass, amidst the gorges which mark the western limits of the great basaltic table- land, where the valley reaches near 6,500 feet altitude. Dr. Hayden has already noted the peculiarities of the basin, attributing its origin to the erosion of the Tertiary lignitic formation, which at a former time doubtless occupied the entire extent of the valley, and stretching far Eastward into what is now comprised in the plains, where its ancient border, if at all recognizable, is obscured by superficial accumulations. Cretaceoufi.- This upper basin is everywhere underlaid by the Cretaceous, the upper deposits of which here consist of heavy measures of shale, with intercalated thin bands of indurated and calcareous matter, attaining approximately a thickness of 800 to 1,000 feet. These deposits have been recognized as the equivalent of formation No. 4 of the series on the Upper Missouri, and it is to their yielding nature that the gentle slopes and comparatively uniform surface which characterize the basin are attributable. In the vicinity of the Cimarron, where they exhibit the greatest vertical extent of any single exposure in the abrupt declivity of the Tertiary plateau, underlying the sandstone of that age, they afford a section of above 500 feet, constituting quite half the entire elevation of these border hills. The deposit is here seen to consist of generally dark- blue shales the upper 190 feet being more of a grayish blue, with little, if any, arenaceous material intermixed. Ninety feet below the base of the Tertiary, concretionary argillo- calcareous masses, generally of small size, are met with, affording fragmentary specimens of Baculites, Inoceramus, &&; and 180 to 190 feet from the top occurs a thin band of shale, from which hare weathered numerous and beautifully- preserved fossils, characteristic of this period. Below the latter horizon there occurs a rather marked band of large concretionary masses, also containing similar fossils to those mentioned above, below which, however, evidences of life are rarely met with until reaching a horizon some 370 feet below the top; and thence 200 feet lower occasional fossiliferous bands occur, always characterized by the peculiar Cretaceous fades of their fauu ® . Between the latter point and the Canadian, twenty- five miles to the east, similar shales apparently compose the bulk of the strata, with, however, as we approach the lower levels, more frequent interpolations of calcareous bands, which often form regular layers of blue argillaceous limestone of a foot or more in thickness. Near Mr. Henry M. Arms's ( Loomis's ranch), a few miles above the mouth of the Vennejo, and near the confluence of Crow Creek, one of these thin limestoue beds outcrops in the base of a low outlying mound, which affords an |