376 DESCRIPTIVE GEOLOGY. 



although Its whole habit and texture have the pecuHar roughness of the 

 trachyte. 



The Tertiary which surrounds this trachyte mass continues up City 

 Creek for about half a mile above it, and then gives out. Its eastern 

 boundary then continues northward, and curves northwest down to the 

 plain, occupying the broad open spurs south of Centreville. To the east 

 of this line, and south of the hills immediately bordering City Creek, the 

 hills from near the mouth of City Creek Canon, east of the grist-mills for 

 about two miles, are occupied by a hard, irregularly-stratified quartzite, 

 which is sometimes almost thinly bedded enough to be called a schist; at 

 others it is in thick heavy beds, 3 and 4 feet through; this is the Weber 

 Quartzite, which has here a strike of north 48° east, with a dip varying from 

 30° to 65° to the southeast. It may be followed along the strike 10 miles 

 in a northeast direction, to where it passes under the horizontal strata of the 

 Vermillion Creek Eocene. Directly north of this, and conformable with it, 

 lie the beds of the Wahsatch limestone, which occupy the summits at the 

 head of Mill Canon, and east of the Salt Lake Tertiary body. These beds 

 here show an estimated thickness of about 6,000 feet, of heavy massive 

 limestone, from which were obtained some Fusilina and other Carbonif- 

 erous fossils. In their upper portion, the limestones seem more impure and 

 siliceous than in the lower. A specimen from one of the beds, about 2,000 

 feet below the top of the series, a gray granular limestone, which weathers 

 an earthy red on the surface, was analyzed by Mr. B. E. Brewster, with the 

 following result : 



Insoluble residue , 2.372 



Ferric oxide and alumina : ■ 0.246 



Lime 53.089 



Magnesia 1.199 



Carbonic acid 42.878 



Water and organic matter 0.216 



100.000 



The dip decreases in passing north and east; from 45° it sinks to 18° 

 at its extreme northeast limit. From stratigraphical position, though with- 



