| OCR Text |
Show 283 acter and mechanical and chemical aggregation of its components. It would appear highly probable that these deposits prove to be identical n age and origin with similar accumulations observed by Dr. Hayden n the plains bordering the foot- hills in Colorado. Besides these, the superficial deposits occurring in the basin proper are all referable to the disintegration of the immediately subjacent strata; and these consisting in the main of the soft Cretaceous shales, the soil resulting plainly bears the stamp of its origin in the extremely finely- comminuted condition of its components, and which are in places mixed with a greater or less percentage of arenaceous material derived from the Tertiary formation. This soil supports a fine growth of the peculiar gramma- grass, which affords throughout the year excellent pasturage. The country is already occupied by many enterprising stock-growers, whose herds and flocks roam the broad plains and are counted by thousands. Along the water- courses, wherever water can be easily conveyed by means of acequias for irrigation, the soil produces abundant crops of corn, the cereals, and various vegetables, demonstrating its fertility and the adaptability of the climate for agricultural as well as pastoral pursuits. Manifestations of igneous phenomena.- Incidental reference has already been made to the basaltic- capped mesas and isolated volcanic cones which constitute the northern and northeastern limits of the basin, and we would here refer to similar deposits and other evidences of comparatively modern igneous activity, which are manifested within the limits immediately under consideration. Forming a natural boundary along the south line of the district, the mesas of Kayado and Qonzalitas extend far out into the plain, above which they rise a thousand feet or more. The great bed of basalt with which their summits are protected once plainly formed an unbroken sheet of igneous matter with that lying immediately to the west, and forming a narrow belt here reclining upon the granitic or metamorphic deposits, which spread over a considerable tract surrounding the Black Mountain group, a section which is intersected by mountain- ridges, marking the denuded crests of gigantic dikes, the evidences of an earlier epoch of igneous activity, a mountaiq-bailding epoch in contradistinction to that in which originated the great basaltic mesas, and still later scoriaceous volcanic cones. It is here these modern and ancient products of igneous activity are most intimately associated; the great Chicorica overflow being some fifty miles distant from the igneous manifestations seated in the main range, with the extensive plateau of the Tertiary intervening, which bears no observed evidence of having been involved in the basaltic inundation, the vestiges of which occupy so large a region to the east and south. While the basin of the Canadian is partially surrounded on two sides by the immense basaltic- capped mesas, the flat summits of which rise 1,000 to 1,500 feet above its surface, the plain itself is everywhere traversed by dikes, the similarity of the components of which would refer them to the same age as that to which belong the enormous overflow in the table- lands. These dikes are of all dimensions, the majority varying in width from 1 to 2 feet, though sometimes much greater, and bearing, if not always, at least in all those at present knowu, nearly east- west. Their presence and course are plainly discernible by the low ridges of dark basaltic debris marking their outcrop in the surface of the plain; in few instances exhibiting rude horizontal crystalline structure, a fine example of which occurs near the southern entrance of the Raton Pass, which has been mentioned by Dr. Hayden. Usually, however, they present an amorphous structure in great variety, |
