67 



plains, and an elevation of 14,500 above that of the sea, in the region 

 where the snow lies all the year. To a person standing in one of 

 these swarms as the.y pass over and around him, the air becomes sen- 

 sibly darkened, and the sound produced by their wings resembles 

 that of the passage of a train of cars on a railroad when standing two 

 or three hundred yards from the track. The Mormon settlements 

 have suffered more from the ravages of these insects than probably all 

 other causes combined. They destroyed nearly all the vegetables 

 cultivated last year at Fort Randall, and extended their ravages east 

 as far as Iowa. 



It must be observed, however, that good grass will generally be 

 found all over these plains, varying in quantity and kind with dif- 

 ferent localities, and that the desert character of the country is not 

 like that found in the deserts on Green river and Snake river, west of 

 the South Pass, where even a sufficiency for animals cannot be found. 



A very different condition of soil, water, and building material of 

 stone and wood, exists when we reach the mountain region. 



The Black Hills, or more properly mountains, lying between the 

 forks of the Shyenne, on the 44th parallel, between the 103d and 

 105th meridians, cover an area of 6,000 square miles. Their bases 

 are elevated from 2,500 feet to 3,500 feet, and the highest peaks are 

 about 6,700 feet above the ocean level. 



The different rocks which compose these mountains, as determined 

 by our exploration, are — 



I. Metamorphozed azoic rock, including granite. 

 II. Lower silurian, (Potsdam sandstone ) , 



III. Devonian? 



IV. Carboniferous. 

 V. Permian. 



VI. Jurassic. 



VII. Cretaceous. 



Ail the rocks below the silurian are igneous and metamorphic, and 

 tiie stratification which they exhibit stands every v/here nearly vertical, 

 with a strike varying between northeast and northv/est. So constant 

 is this vertical dip, that it may not in reality indicate primary stratifi- 

 cation, but some mechanical arrangement due to the molecular forces 

 brought into existence during its cooling from the heated state. 

 All the rocks, from the silurian to the close of the cretaceous, ajjpa- 

 rently lie conformable to each other. The shape of the mass is ellip- 

 tical. The direction of the longest line of this or major axis being 

 about north 20° west. On the west the rocks dip, as a whole, very 

 gently, and at a distance of five miles from the foot of the hills the 

 cretaceous is apparently undisturbed, though at tlie base these rocks 

 In some places stand at an angle of 45°. The manner in which this 

 rock lies suggests the idea that the cretaceous probably forms a con- 

 siderable portion of the elevated plateau between the Black Hills and 

 Big Horn mountains. The dip of the upheaved rocks on the west side 

 is as a whole very gentle, not amounting to more than from 5° to 15°, 

 and consequently they are considerably developed, and form more than 

 one-half the mountain mass composing some very high ridges. These 

 rocks have a much greater inclination on tlie east side of the moun- 



