LA2fD AREA IN THE CARBONIFEROUS. 181 



tirnhdiis establishes the Carboniferous age of the quartzite. After the Dia- 

 mond Peak quartzite attains a thickness of 3,000 feet, a change sets in with 

 ahernating beds of coarse shales and conglomerates more or less mixed 

 with calcareous sediments, the entire series being admirably exposed at the 

 base of the Lower Goal-measures on the southwest slope of Richmond 

 Mountain. Here we find positive e%'idence of the existence of fresh-water 

 shells associated in the same beds with plant life fairly well preserved, 

 although specific determinations are impossible. This is the only instance 

 yet discovered of the existence of fresh-water species in the Paleozoic 

 rocks of the Great Basin, and points conclusively to the existence of a land 

 surface at no great distance and long after the White Pine shales had been 

 bm-ied beneath 3,000 feet of sands. Even if they had been deposited in 

 an estuarv and washed into their present position by rapid currents the 

 land area could not be far awa}'. This grouji of rocks carrying a fresh- 

 Avater fauna soon liecomes submerged beneath the limestones of the Lower 

 Coal-measures, which occupy such widespread areas of the Great Basin and 

 Avhich, so far as the physical conditions of deposition are concerned, closely 

 resemble the Nevada limestone. 



Additional evidence of laud areas during the Carboniferous is found at 

 Pancake and Bald Mountain, a somewhat similar series of strata occurring 

 in both localities, with well developed coal seams, bituminous shales, and 

 evidences of plant life both above and below the coal. 



Next in turn overlying the Lower Coal-measures occin-s the Weber 

 conglomerate, a formation 2,000 feet in thickness, of coarse siliceous mate- 

 rial made up of pebbles varying in size, composed of quartz, jasper, chert, 

 and lionistone, unquestionably an off-shore deposit in shallow water. Such 

 coarse material could not have been transported any great distance. 

 The conglomerates of Agate Pass, in the Cortez Range, and at Moleen 

 Peak present identical physical conditions with CAadences of the same 

 oif-shore de])osits. To the eastward, removed from the continental area, 

 the sediments of this epoch become finer grained and arenaceous in tex- 

 ture. How long a time was occupied in the accmnulation of this great 

 thickness of siliceous pebbles it is of course impossible to say. Finally it 

 was followed by a suVjmergence accompanied by a deposition of limestone 



