250 GEOLOGY OF THE HIGH PLATEAUS. 



where described as of middle or late Eocene age. The case is also pre- 

 sented 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 Cafion, 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 mid- 

 dle 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 attri- 

 tion, 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 pro- 

 cesses which have accumulated both. 



No sedimentary formations are found in the northern part of Grass 



*In tho West, a marsSiy locality formed by tho accumulation of vegotablo mold and river silt, 

 yielding a peculiar wild grass, Is called a "meadow." In a moister country it would be simply a bog. 



