SUMMARY 241 



6. The western lake had 5 feet of evaporation and 1 foot of overflow 

 per year, and this was supplied by 10 inches of rainfall and 5 feet 2 

 inches of inflow from the drainage basin. 



(Note. — With a 15-inch rainfall and 10 inches of run-off, about the 

 same as the headwaters of the Missouri today, the drainage basin would 

 luive to be a))out 50,000 square miles in extent, or lialf the size of tbe 

 State of Wyoming.) 



7. The 1 foot of outflow per year from 8,000 square miles would sup- 

 ply the inner lakes, with an area of 2,000 square miles, with l feet of 

 water per year; the rainfall would supply 10 inches and the water level 

 would remain about constant, with an evaporation of 5 feet per year, 



8. The concentration in the lakes was about 1 part gypsum to ;)()0 

 parts water 1)y volume at the end of 3, and 4 feet of watei- coming in 

 fruni the overflowing lakes would add 1 foot of gypsum every 75 years 

 to the inner basins, or 5 feet in 375 years.^° Correcting this for the 

 decrease in concentration of the outer basin waters, it would take about 

 500 years to add the 5 feet of gypsum. 



9. If the inner basin was 1,500 feet deep, there was enough water in 

 it to supply 5 feet of gypsum. Total of 10 feet of gypsum at the close 

 of 8. 



10. Time for 4, 260 veais; for 8, 500 vears. Total time. :(iO vears. 



11. The thin deposits over 8,000 square miles nuiy have originated by 

 piccipitation from shallow concentrated waters soon after 3 and the pre- 

 cipitation liave lieen interrupted l)y inflow from riveis. 



Summary 



Tlic iiiiiiii (liHirult ics in exphiining thii-k ileposits of gypsum were 

 stated oil ihe lirst page of this paper. 



1. The \o!iiiiie of water for the thicknesses of gypsiiin greater than Id 

 feet is not e.\phiiiie(l hv the pre>eiit h\potheses. excepting h\ having 

 hasjiis (lee])ei' than 1.5(i() feet or hv ha\iiii; a higher proport idn of caiciiiiii 

 sulphate to sodimn chh»ri(h': hut it is shown that such (le[)osit- lie in 

 basins just enough helow the sni KniiKhngs to contain the extra thickness, 

 and that the givater thickness may have resulted from currents shifting 

 the unconsolidat('(l i:vp>iiiii aloni;- the bottom. 



'"If llic DiiliT liil<cs wcrt' .")(M) feci ilrc|i :inil llhTc \\;iv mu' I'ikiI iif (i\ I'l'lluw per vciir. 

 Ilicli- wjilfi's WDiild he piaci iciill.v one hair iis ciiiicinlrM led Ml iln- cikI ol' ."lUd vi'ius as at 

 llif bi'niiiiiliiK. ami iIk' aiiiuinil ul' jiypsuiii cariii'd Im i lif inner liasiiis would Im> tliree- 

 lOiirtlis as ninili in ."lOli years as il' Ihe cuncen Oa I imi Ilk! remained Ihe same as In the 

 he^innlnn. 



