THE AWAPA PLATEAU. 



275 



ing range in the superficial aspects of the beds. In the northern part of the 

 plateau the dark argilloid and hornblendic trachytes predominate. They 

 agree in their characters and aspects with those which occur in the Fish Lake 

 Plateau and Mount Marvine. There is also decided evidence that the 

 main sources from which they outflowed were around the southeastern bor- 

 ders of the lake. This evidence is substantially the fact, that the sheets 

 increase in thickness and become more rugged in that quarter, and all the 

 phenomena of flow indicate movement from that direction. The supposed 

 location of the vents, however, was not visited. No augitic andesites were 

 noticed intercalating with the northern trachytes of the Awapa, though 

 large bodies of them may have escaped observation, owing to the supei-ficial 

 and cursory character of the investigation. 



No conglomerates or tufas were seen in the northern part of the Awapa, 

 and these would have been noticed if they really exist there in masses of 

 any importance. As such bodies are usually very bulky and conspicu- 

 ous, it is hardly possible to overlook them. In the western part of the pla- 

 teau, however, they are found in great volume. They are stratified in the 

 usual manner, with nearly horizontal bedding or with that peculiar cross- 

 bedding which may be seen in Panquitch Canon (Heliotype No. 4). In 

 the western wall of the plateau, a little north of East Fork Canon, these 

 conglomerates form a grand cliff and talus rising about 3,400 feet above 

 Grass Valley, and the total thickness of the fragmental beds is roughly 

 estimated at 1,600 feet. Large masses of hornblendic trachyte are found 

 beneath them, and granitoid trachyte above them. These beds of conglom- 

 erate stretch north and south from this point, forming the most conspic- 

 uous part of the plateau wall, for a distance of 21 or 22 miles. Their deg- 

 radation gives rise to a precipitous escarpment, broken in several places by 

 ravines and gorges. They are also found in great bulk in the canons which 

 cut into the heart of the plateau. They are believed to be alluvial in their 

 origin. The fragments which they contain are exceedingly varied in their 

 composition and texture. Hornblendic andesites and trachytes are commin- 

 gled in the same stratum, and of each kind there are very many varieties. 

 In one of the deeper canons some propylitic fragments were found, but 



