CONDITIONS NOT EXPLAINED BY HYPOTHESIS 227 



cally the same amount as oalcinm sulphate, and if the concentration took 

 ])lace from fresh water in inclosed basins, limestone of practically the 

 same thickness as the g}'psum should be present with the gypsum. But 

 limestone is rarely associated with the gypsum and is never interbedded 

 with it, as would necessarily be the case unless the gypsum and lime 

 were deposited together and the resulting rock were a mixture. 



In the waters of Great Salt Lake, Sevier Lake, and other lakes of high 

 concentration little or no calcium and CO3 are present. Clarke says that 

 "all of the waters tributary to Great Salt Lake, so far as they have been 

 examined, contain notable quantities of carbonates, which are absent 

 from the lake itself. These salts have evidently been precipitated from 

 solution, and evidence of this process is found in ])eds of oolitic sand, 

 composed mainly of calcium carbonate, which exist at various points along 

 the lake shore." ^^ 



Lake Lahontan, with watci-s of a siliiiity one-fifth to one-tenth as high 

 as the Great Salt Lake, has already had most of the lime salt thrown 

 down as tufa, while the SO^ content remaiiis liigh. Lake Lahontan 

 represents concentration of fresh waters, but as its ili-ainage basin is 

 largely composed of igneous rocks, the sulphates would probably be lower 

 Ihan in the fresh -water pools postulated. 



WHAT BECAME OF THE SODIUM CHLORIDE AND OTHER SALTS? 



Deposits of salt are not mentioned in connection uiili tlu' upper llr^l 

 Beds, but it is frequently equal in amount to gypsmn in streams in arid 

 regions and probably averages one-half to one-fourth as al)undant. As 

 no salt beds occur, the solutions must have remained considerahly above 

 saturation, ami ')i> to 100 feet of water must have been left in eaeli pool 

 to contain the salt ; but it seems almost certain that some ]Wols woulil 

 have dried up and the more soluble salts have been precipitated. Some 

 salt may have been deposited and redissolved, !)ut there are no t'\ idences 

 of this in the rocks, and waters from wells ]»enetrating tlie l)eds do not 

 carry unusual quantities of salt. If some of the pools had dried up, a 

 series of alternating \H'i\<- of \ai'ious salts wouM lia\'e been foi-nuMl : but 

 such deposits ai'e ne\cr found in the T»cd Ileds. 'I'lie waters e()uld not 

 escape fi'oni the region without reuniting, and if they reunited and 

 were di-ainc(| hy land \\;ir|)ing. a large pari of the region must have been 

 submergeil and suha(pieous deposits must have heen loi'me(| over the 

 gypsum. 



=»U. S. Geol. Siiiv. IJiill. i<M, p. ]4<i 



