186 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. 



associated sands are distinctly bedded. They lie in a nearly horizontal 

 position, or at a low angle of deposition, resting upon the upturned edges 

 of the Laramie rocks. 



Local faulting and displacement in the conglomerate may be observed, 

 but this may be attributed to fracturing and slipping of limited masses, due 

 to the wearing away of underlying beds or to ice filling the numerous cracks 

 and ravines found in the rock mass, causing landslides on a grand scale. 

 That the conglomerate has been subjected to great pressure and movement 

 within the mass is everywhere apparent by the action of the quartzite 

 pebbles on one another. Field study of these pebbles is most interesting 

 from the curious modifications they have undergone under pressure. In 

 some instances they are flattened and rolled; in others they are indented 

 and forced one into the other. Many of these pebbles are cracked and 

 crushed, in some cases almost ground up, so great has been the pressure 

 exerted upon them. It is curious to observe how these flattened, almond- 

 shaped quartzite pebbles, with the pointed end fractured, have been sharply 

 cut off by dislocation and movement of the mass. Many of the smaller 

 fractured pebbles have smooth surfaces, as if cut off by some sharp instru- 

 ment. A vast number of the pebbles show a peculiar mottled appearance, 

 being covered by white spots of varying size, probably produced by pres- 

 sure of the pebbles against one another. 



The top of Pinyon Peak is capped by a heavy bed of dark basic brec- 

 cia, made up of angular fragments in every way resembling the breccia, 

 already described, at the junction of Coidter and Wolverine creeks on the 

 west and Two Ocean Plateau on the east. 



According to Professor Iddings, who studied the west slope of the 

 peak, the breccia is 300 feet thick. It rests directly on the conglomerate, 

 stretching for nearly half a mile along the east face of the mountain, 

 projecting out like a lava flow over several of the characteristic long ridges. 

 On the west side of the peak it stretches westward or terminates abruptly, 

 with the conglomerate coming to the surface from beneath the breccias. 

 The conglomerate was evidently deposited before the laying down of the 

 breccia. No animal or vegetable remains have as yet been found in these 

 conglomerates and indurated sandstones, consequently no definite state- 

 ment can be made as to their precise age. That they are young*er than the 

 Laramie rocks is evident, as they were deposited unconformably upon the 



