| OCR Text |
Show 250 GEOLOGY OF THE HIGH PLATEAUS. where described as of middle or late Eocene age. The case is also presented where the same stratum, traced horizontally along its exposure, passes gradually from one kind into the other. These beds are probably of greater antiquity than the Bonneville beaches around the shores of Great Salt Lake, being in a much more dilapidated condition and only occasional remnants being preserved. Near the head of East Fork Canon, a large "meadow"* or bog, formed by the accumulation of the finest river silt, deposited by slack water, still indicates the recency of the same struggle between the uplifting of the plateau tending to dam the stream and the agency of the running water in carving its channel and lowering its outlet. Perhaps the most striking phenomena which may be seen in Grass Valley are the great alluvial cones now forming in the northern and middle portions of it. The great gorge of the Fish Lake Plateau opens into it near the northern end, and a very flat cone, with a radius nearly 3J miles in length, has been built of the detritus brought down from that chasm. Viewed from the summit of that table, which rises 4,300 feet above it, the periphery of the cone is seen to be very nearly circular through an arc of about 120°, becoming confluent with another great cone south of it. Many others of equal magnitude and quite perfect in form are displayed down the valley, most of them sloping from the Sevier side. They are composed of fragments which are not much abraded or rounded by attrition, and whatever waste they have suffered seems to be due as much to slow weathering as to abrasion. They are held in a matrix of soil which is highly fertile when watered, but too stony for the plough. They vary in size from a few ounces to a few pounds, and near the apices of the cones they are found weighing many hundreds of pounds. At numerous places the shiftings of the streams have enabled them to cut into the cones locally, and the sections always reveal a pronounced stratification. Comparing them with the ancient conglomerates now exposed in the plateau walls on either side of the valley, it is impossible to doubt the identity of the processes which have accumulated both. No sedimentary formations are found in the northern part of Grass * In the West, a marshy locality formed by the accumulation of vegetable mold and river silt, yielding a peculiar wild grass, is called a "meadow." In a moister country it would be simply a bog. |
