224 E.. B. BRANSON ORIGIN OF RED BEDS OF WESTERN WYOMING 



above which the fall is 55 to 63 feet per mile, the run-off measured in 

 1897 was 70 per cent of the rainfall.^"' llelatioiis of like character hold 

 for nearly every river that leaves the mountains and flows across the 

 more arid plains. A run-off of 30 to 70 per cent is to be expected of 

 streams emerging from mountain regions and of 1 to 20 per cent for 

 streams that have run for some distance through arid plains.^* 



MATERIALS IN SOLUTION IN RIVER WATERS 



When waters from the upper reaches of rivers are analyzed they gen- 

 erally have only a small amount of mineral matter in solution and show 

 iriore and more concentration as arid plains are crossed and the water 

 taken by evaporation is replaced from underground sources, but salinity 

 may decrease or increase if the stream continues to flow through arid 

 plains. 



The Arkansas Eiver has a salinity of 148 parts per million at Caiion 

 City, Colorado, where the run-off is 20 to 30 per cent; 2,134 parts per 

 million at Eoeky Ford, Colorado, and an average of 630 parts per million 

 at Little Eock, Arkansas. ^^ 



In streams flowing over sedimentary rocks in arid regions the sulphates 

 frequently become more abundant than the carbonates. Clarke says:'" 

 ''In arid regions sulphates and chlorides prevail." But on an average 

 the sulphates are only slightly in excess of the carbonates. 



The region postulated consisted of horizontal sandstone, probably 

 poorly consolidated, with an area of some 40,000 square miles and with 

 slight relief. No stream analyses from such a region are available, but 

 it is probable that stream data from the loveler parts of Wyoming, where 

 the rocks are sedimentary, will answer as well as any to be found. 



Slosson^^ g'wes six analyses of waters from the Popo Agie Eiver, 

 Laramie Eiver, and Little Goose Creek, streams that occur in the region 

 under discussion and are typical of it. The Popo Agie analysis is of 

 waters emerging from the mountains into the plains niid the Laramie 

 and Goose Creek analyses are of waters that have run for some distance 

 through arid plains. 



In stating the analyses in hypothetical combinations, Slosson gives 

 calcium sulphate in the Laramie Eiver only, and three out of five analyses 

 f]-om it show none. Eecalculation of tliree of Sk)sson's analvses of waters 



" Ibid., pp. 56-57. 



"Water Supply Paper 306 of the U. S. Geological Survey contains maps, plates 1 and 

 2, showing relationship of run-off to precipitation. 

 i» Clarke: Bull. 11. S. Geol. Surv., 491. p. 70. 

 " Ibid., p. 81. 

 1" Wyoming Experiment Station, Bull. 24. 



