18SG.] KEW YORK ACADEMY OF SCIENCES. 125 



City trail to mouth of Po'keepsie Gulch gives us four miles of 

 eruptive rock; and two miles of quartzites of various colors 

 bring us to the Uncompahgre Bridge, where we join our section 

 made along Mineral Creek. Just as we dip into Ouray we see a 

 ridge of limestone crossing the highway. On the south side it 

 is highly altered. On the north side it is nearly horizontal. 

 So, also, are all the rocks and cliffs on both sides of the river 

 going north. The famous Mineral Farm mine is probably 

 on tills limestone. 



Ouray is situated in a cul-de-sac caflon with cliffs of arenaceous 

 rocks rising to the height of 2,000 feet. These form remarkable 

 scenery; they repose nearly horizontal, and are of various colors. 

 They have many entering and projecting angles of perpendicular 

 ii^sures forming buttresses and bay-window projections, titanic 

 walls, with watch towers and sentinel boxes. 



Fig. 3.— Section ok Hills at Camp Paquine. 



R, Uncompahgre river; C, Carboniferous sandstone; L, Limestone (argentiferous); 

 P, Porphyry. 



At Ouray begin the northern troubles of the mountains. 

 Here are fissures of great magnitude, faults, downthrows and 

 upthrows. Through fissures issue hot springs — degenerate re- 

 mainders of former grander springs. 



Trachyte has followed us all the way from Silverton, capping 

 the summits of all the mountains we have passed. We go down 

 this valley a few miles and see the mountains fall off into hills, 

 and hills merge into mesas. Two miles below Ouray we find 

 silver in new geological horizons. 



One of the layers of rock composing the cliffs is a black, sandy 

 limestone or dolomite. Above it lie horizontal unconformable 



