| OCR Text |
Show 98 been given in a previous report. A mile below Pueblo a bed of about r> 0 feet in thickness is exposed, which consists in alternate layers of gypsum and clay, each nearly a fifth to a third of au inch in thickness. Now, if we consider the periods during which the clay or mud was deposited as the rainy seasons, in which the streams carried much muddy water from the mountains into the neighboring shallow sea, and the following deposition of gypsum as the result of the waters being clear and more concentrated, as would be the case in a dry season, or in summer, we then have for each alternate layer, one year, and for the deposition of the bed of 50 feet, a period of twelve hundred years. The position of the strata along the valley has not been disturbed by violent action like volcanic eruption, < fcc, and therefore occupy a horizontal position. Here and there, however, singular bends are observed in the strata, the limestone layers beiug slightly curved. Another irregularity is, that I observed, four miles above Pueblo, the deposits appearing as though formed under peculiar influences, as currents or motions of some kind. These irregularities, however, cover but a small area, the neighboring strata being quite regular. This figure represents a section of the Arkansas Valley, five miles above Pueblo, Colo., which shows irregular stratification. A, sandstone ; D, saudstone interstratified with slate; C, slate; B, limestone. Distance a b = 200 yards; height C H = 30 feet. Here and there white efflorescences are noticed in the valley of the Arkansas. These, on examination, were found to consist of sulphate aud chloride of sodium. A number of mineral springs occur in this section- one at Carlisle, and more than half a dozen at Canon City- descriptions of which, with analyses, were given in a former report. The water of all wells sunk in the valley is gypsiferous- usually called in this section ' » alkaliue water." Whether or not the use of this water will prove beneficial to health is yet to be seen. Here aud there the slopes of the Arkansas Valley are densely covered with drift and bowlders of no small size. THE SIEKltA MOJADA AND SANGRE DE C1IISTO MOUNTAINS. The Sierra Mojada ( also called Cuerno verde range and Greenhorn Menu tains, at least as far as its southern portion is concerned) is nearly parallel for fifty miles with the Saugre de Cristo Mountains, and thus is formed a long'valley between the two chains, which is draiued by a number of creeks. The most northern portiou of this depression is known by the name of* 4 Wet Mountain Valley," while descending in a southerly direction we have the valley of the Muddy and that of the Hnerfauo, ( Huerfano Park.) The Saugre de Cristo Mountains are joined on the west side by a wide, plain- like valley, the San Luis, while the Sierra Mojada forms the western boundary of the great plains of Southeastern Colorado. Where the plains approach the mountain range a great number of trachytic dikes protrude through the sedimentary strata. Where the mountains die out in the plains, the strata of the cretaceous epoch occupy the field almost exclusively, while between the foot- hills of the mountains carboniferous rocks are exposed. The chief mass ot the mountaius, however, is composed of azoic rocks. These masses of granites and gneisses aie Hill of volcanic dikes. Near the junction of the Saint Charles aud Green- |
