INDIAN CREEK LACCOLITH. 13 



these limestones is also included in the laccolithic mass separating the igne- 

 ous rock into the two sheets, whose southward extension has already been 

 noted at Trilobite Point and the South End Hills. 



On the southern side of the mountain the lower intruded sheet rests 

 directly upon the crystalline schists, and as we pass up the southern slope 

 of the mountain, which is precipitous in places, we find a layer of limestone 

 about. 300 feet thick, which is not wholly continuous. Above it are several 

 hundred feet of porphyry, and then a bluff wall of 200 feet of limestone 

 that forms the surface of the table-topped portion of the mountain, upon 

 which rises a cone of limestone 400 feet in height. The limestone has a 

 slight dip southward, which brings the porphyry out at a higher altitude 

 on the northern side of the peak. The character of the limestone overlying 

 the porphyry is the same as that of the limestone on the northern side of 

 Indian Creek, which occurs in the same position, and which has been iden- 

 tified as Middle Cambrian. As these beds approach the eruptive mass 

 forming the peak southwest of The Dome, they turn up abruptly to a steep 

 angle, dipping away from it toward the northeast at 55°. 



The steep northern face of The Dome, below the flat top, is almost 

 wholly andesite-porphyry to within 300 feet of the bed of the creek; the 

 lower part being limestone, forming steep walls that rise above a bench of 

 gneiss. A thin belt of shale or limestone occurs about halfway up the 

 slope, inclosed in the porphyry. It does not appear to be continuous 

 horizontally, though quite persistent. The contact between the rocks just 

 described and the intrusive mass to the west is sharply marked and nearly 

 vertical, and will be described in connection with the occurrence of that 

 rock body. 



The limestone underlying the andesite-porphyry at the northern base 

 of The Dome is in nearly horizontal beds, but at the eastern base of the 

 mountain the gneiss rises up and cuts it off. At a higher altitude the lime- 

 stone is exposed with a steep westerly dip, evidently bent and faulted, with 

 a throw of several hundred feet. At about this place the lower sheet of 

 porphyry cuts down to the horizon of the gneiss. 



INDIAN CREEK LACCOLITH. 



North of the valley of Indian Creek the slopes rise steeply upward to 

 the base of a wall or cliff that extends westward from the eastern face of 

 the mountains to the head of Indian Creek Valley. The lower part of this 



