216 IRVING. 



distance of twenty-two feet, still dipping away from the moun- 

 tain, but at a lower angle than before. 



A glance at the illustration (Fig. 9) will at once show that it 

 is impossible for so great a thickness of shale to have passed up 

 between the limestone and the phonolite in such a way as to 

 entirely cover the hill, and it would seem to be necessary to as- 

 sume the existence of a fault along the northern limits of the 

 phonolite in order to explain the facts. 



In the crater-like depression on the other side of the moun- 

 tain the writer was able to find no exposures of shales on ac- 

 count of the great depth of talus, although such have been re- 

 ported. 



A small exposure of Cambrian shales was found at about the 

 center of the connecting ridge between the two triangular ends 

 of the mountain. They rest horizontally upon the phonolite 

 on the very edge of the inside cliff that forms the northern wall 

 of the depression, and attain only a thickness of two or three 

 feet. . 



At the head of Calamity gulch near Ellington's cabin a drill 

 hole was sunk to a depth of three hundred and seventy feet ; 

 it passed through phonolite for the entire distance, and did not 

 penetrate into the shale below. A glance at the model (Plate 

 XIV) will show that the sediments come into close contact 

 with the phonolite escarpment on the north and west, but are 

 comparatively far removed from it on the south and east, where 

 they are exposed on the opposite side of the broad, peripheral 

 valley that extends around the mountain on these two sides. 

 In the bottom of this valley on the south the drill core men- 

 tioned above has been sunk in the phonolite, and a small rim of 

 shales is seen between this and the limestone on its southern 

 border. On the east the limestone is exposed in the ridge 

 running out from Elk mountain, and between here and the 

 escarpment the phonolite is visible in the "Spook" shaft. 

 Shales if present are obscured by vegetation and talus. 



In neither of these two limestone exposures can an appreci- 

 able dip be observed, but as one stands on top of the mountain, 

 a slight incline toward the south and east seems to be present. 



