OCR Text |
Show THE SHINAKTJMP. 147 owing to the gradual transiticfri into the Vermilion Cliff series above. Disregarding the doubtful horizons, the thickness along the Hurricane ledge is not far from 1,300 feet, and somewhat less at Kanab ; and, in general, it attenuates very slowly and gradually as we recede southeastward, though it never sinks to small proportions anywhere within the limits of the Plateau Country. Besides the transitional shales above, there are three subdivisions. Commencing at the base, they are as follows: 1. Silico-argillaceous shales........................................ 450 to 650 feet. 2. Belted, highly-colored arenaceous and siliceous shales............ 400 to 500 feet. 3. Brown sandstone.............................................. 150 to.250 feet. The thickness of the transitional shales up to the base of the Vermilion Cliff sandstone may be reckoned from 550 to 750 feet. Within these shales there often appears a singular conglomerate. It consists of fragments of silicified wood imbedded in a matrix of sand and gravel. Sometimes trunks of trees of considerable size, thoroughly silicified, are found, to which the Piute Indians have given the name "Shindrump," meaning "the weapons of Shinav," the wolf-god. The conglomerate is found in many widely-separated localities, with a thickness rarely exceeding 50 feet. It occasionally thins out and disappears, but usually recurs if the outcrop be traced onwards, resembling the mode of occurrence common to the coal-seams of the Carboniferous coal measures. It is the most variable member of the Shinarump thus far observed. It is found on the west flank of the Markagunt and throughout the great circuit of cliffs south of the High Plateaus ; it is seen at Paria, and again at the Ped Gate between the Aquarius and Thousand Lake Mountain, the characters of the formation being quite the same in all these localities. The conditions under which it was accumulated would seem to have been remarkably uniform, and may have been similar in some respects to those attending the formation of coal. The subsequent silicification of the wood upon a scale so extensive arid even universal is certainly a very striking phenomenon, and one for which no explanation suggests itself. It may be of interest to mention that at Leeds, in Southwestern Utah, the fragments of silicified wood were found to be strongly impregnated with horn-silver. Subsequent prospecting, which had been stimulated by this curious discovery, led to the finding of horn^silver |