302 GEOLOGY i)V THE BLACK HILLS. 



It is (loiiljtl'iil it" tlicre is a lieavy snow-fall in the Black llilLs. The 

 miners who remained in the Hills during the winter of 1874-5 report that 

 ther(i was never more than six inches of snow on the ground until April, 

 when a heavy fall occurred at the time they were removed by Capt John 

 Mix. 



In a few localities in the interior of the Hills I saw small trees which 

 had been bent down by snow-drifts, but the streams showed no traces of 

 freshets caused by snow melting in the spring. There was no drift-wood 

 along their banks, and the bridges built by General Custer the previous 

 summer were still in place, which a rise of a few inches would have swept 

 away. The snow must be sometimes deep enough to hide trails and land- 

 marks, as the main Indian trails leading through the Hills were marked by 

 stones placed in the forks of the trees or by one or more sets of blazes, the 

 oldest almost overgrown by the bark. 



No hail-storms occurred in the Hills the past summer, which caused 

 an injury to vegetation. Often during thunder-storms it would hail for a 

 few minutes, owing to some sudden change of temperature in the storm. The 

 central portion of the Hills is elevated from 2,000 to 3,000 feet above the 

 foothills, or an altitude of 5,000 to 7,000 feet above the sea, and necessarily 

 the weather is sensibly cooler. The thermometer seldom stands above 85° 

 Fahrenheit in the shade. In this elevated region thin ice formed occasion- 

 ally at night in open dishes of water left exposed to the sky even in mid- 

 sunnner, and after September 1 thin ice formed nearly every night in still 

 pools. This low temperature occurred just before daylight and was of 

 short duration. It was owing to the great radiation and evaporation, due 

 to the rarity of the air and the clearness of the sky, causing no correspond- 

 ing reflection of heat back to the earth. It seemed to have no bad effect 

 on vegetation, which flourishes bright and green until about September 8, 

 when the first frosts began to change the color of the leaves of the plants. 



The growing season in this elevated region is necessarily but a few 

 months. June 10 the aspen trees at the head of Floral Valley, at an alti- 

 tude of G,G00 feet, were just bursting into leaf, the grass was green but 

 quite short, and by September 8 the plants in this same valley were col- 



