308 GEOLOGY OF TBE BLACK HILLS. 



regular suj)ply of moisture for their maintenance, gi'owing on (hy, rocky 

 hill-sides, ex])osed to parching winds and the heat of the sun, and flourish- 

 ing and producirig flowers and seed in perfection. On the tops of the 

 mountains, near Harney and Custer Peaks, far above the level of any 

 springs of water, I found patches of wild raspberries growing so thickly 

 that the ground was covered with them. The bearing-canes, which are of 

 a previous year's growth, were of full size and loaded with fruit, showing 

 that the previous season had been equally favorable to their development. 

 All along the eastern slope of the Hills burr-oak and elm trees, which 

 require an abundance of moisture to sustain their growth, attain at least a 

 medium size, and are found not only along the banks of the running 

 streams, but growing in small grooves on the hill-sides and in the swales and 

 valleys. On examining the pine timber in diff'erent parts of the Hills I 

 found that the annual rings of growth were uniform in width. The coarse- 

 ness of the grain of the timber, its softness, and the regular appearance of 

 the full-grown trees, all indicate, independent of the species of tree, a 

 uniform yearly growth, and consequently a regular rain-fall. From these 

 evidences I think I may safely draw the conclusion that the season of 1875 

 in the Black Hills which 1 witnessed was not an unusually wet one, 

 although the rain-fall may have been somewhat above the average. The 

 average amount of rain for the plains surrounding the Black Hills does not, 

 probabl}', exceed 15 inches for the whole year. To the north, in the 

 valley of the Upper Missouri, it is about 12 inches. 



From the nature of the work the past season it was impracticable to 

 definitely determine the amount of rain-fall ; but the presence of trees indi- 

 cates conclusively that it must be at least 25 inches, and not much below 

 that amount for more than a single successive season, or many of the trees 

 would perish from want of moisture. The following tables, giving the rain- 

 fall in inches for the nearest localities to the Black Hills wdiere observations 

 have been made, are from the Smithsonian Institution tables and the records 

 of the Signal Service of the United States Army: 



