3 1 2 GEOLOGY OF THE BLACK HILLS. 



iiiid streams of considerable size, and but a few miles apart, drain this 

 region, affording a constant and regular supply of water for both stock- 

 raising and nn'ning ])iirposes. 



The creeks which drain the gold field rise in numerous small springs, 

 issuing from the granite and metamorphic rocks, and the water is conse- 

 (juently remaikably pure and free from mineral or organic matter. Those 

 branches which head in the great Carboniferous limestone yield water 

 suitable for most domestic purposes, the only drawback being a slight 

 " hardness," due to the presence of carbonate of lime, which does not in 

 the least affect the health of those using it. 



Only among the foothills, where the gypsum of the Red Beds or the 

 " alkali" derived from the Jurassic and Cretaceous shales has contaminated 

 the streams draining these formations, is the water found to be unfit for 

 cooking purposes and possessing purgative properties. Elsewhere through- 

 out the whole area of the Black Hills included within the timber-line at the 

 edge of the sunounding plains the water, both of the springs and running 

 streams, is clear, cold, delicious to the taste, and extremely healthy. Early 

 in June the temperature of the springs at the head of Floral Valley was 

 found to be 39° F., tbe elevation being 6,600 feet above the sea. In mid- 

 summer the water of a number of springs in the inteiior of the Hills was 

 tested with an accurate thermometer, and found to vary between 42° and 

 44° F. After August 1, the past summer, the volume of all the streams in 

 the Black Hills was somewhat diminished by the partial cessation of the 

 heavy rains, but none of the creeks stopped running, except that portion of 

 French Creek above the Stockade, where the springs supplying the water 

 are small and the grade very slight. From the character of the geological 

 formations outcropping in the foothills and along the edge of the plains, all 

 the streams rising in the Black Hills sink in their beds and disappear before 

 passing through the belt of Carboniferous limestone, with the exception of 

 Rapid Creek, which flows into the Cheyenne, and Spearfish and Redwater, 

 vrhich empty into the Belle Fourche. Large springs of good cold water 

 burst out from under the Triassic limestone in the Red Beds at intervals 

 along the inner rim of the broad Red Vallev encirclinor the Black Hills. 

 These springs will be very valuable to the future stock-raisers in this region. 



