1891.] NEW YORK ACADEMY OF SCIENCES. 59 



die, and South butfces, the two latter being striking in appear- 

 ance, forming steep, rugged cones, while the North Butie is 

 somewhat less precipitous and covers more ground. Leaving 

 the railroad survey at a point three thousand feet above the sea 

 level, the prairie rises gradually some nine hundred feet in thirty 

 miles. There are no signs of civilized life in this whole district, 

 excepting that as the hills are approached there are remains of a 

 Government corral, suggestive of Indian days, and the homes of 

 one or two settlers upon the head waters of the creeks appear. 



The prairie is strewn with glacial drift bowlders — apparently 

 of quite recent deposition, as they are so little embedded in the 

 soil — with sharp angles and edges, consisting of porphyry and 

 syenite. There are no rocks in place, save here ami tliere where 

 streams have cut into the prairie; these are soft, calcareous and 

 clay sandstones and shales, evidently very late Cretaceous or Ter- 

 tiary. Upon reaching the most easterly butte it is seen to be 

 divided into several peaks, the most sontherly and most promi- 

 nent being called locally "Mt. Morris." Approaching this 

 mountain the ground is thickly strewn with every kind of ig- 

 neous rock — dark green basalts, phonolite, and every variety of 

 feldspathic porphyry. The summit of Mt. Morris I found by 

 observation to be six thousand three hundred feet above sea level 

 and two thousand four hundred feet above the old Government 

 stockade. The mountain mass, like that of the two other buttes, 

 is a grayish porphyry containing small feldspar crystals, but 

 gHshed and seamed by dike after dike of trap and large crystal 

 birdseye porphyry. Between these dikes are older clay slates, 

 mica schists, hornblendic schists, all inclined at a sharp angle 

 against the mountain, and indicating clearly the intrusive char- 

 acter of the mass. 



The quartzite carries free gold in considerable quantity, and 

 where crossed by mountain streams some very rich pay gravel 

 is found, which, owing to the scarcity of water, can hardly 

 become available ; but I was informed tiiat miners have carried 

 it down the hill and washed it in the Cottonwood with profit. 

 The decomposed and altered slates also gave evidence of gold, 

 but no development had been instituted. Here and there 

 along the hillside were float masses of manganese and bowlders 

 of magnetic iron, but the most remarkable and interesting 

 feature, geologically, is a collar of limestone surrounding the 

 . mountain about two-thirds of the way up. This limestone 

 belt is nowhere wider thpn seven hundred or eight hundred feet, 

 but forms a complete circle, excepting upon the southern slope, 

 where it is either broken or its continuity concealed by the 

 talus from the porphyry cliffs above. It is highly metamor- 



