378 DESCRIPTIVE GEOLOGY. . 



corrugated body; soil and a dense growth of scrub-oaks preventing obser- 

 vation of the exact contact. Yet, from the nature and position of the two 

 bodies, there is no doubt that they are actually unconformable ; and they 

 may, therefore, be considered to represent the one the Huronian, and the 

 other the Laurentian, member of the Archaean. 



The whole sedimentary series, from the Weber Quartzite down, there- 

 fore, appears in the gap between the two masses of Tertiary, that which lies 

 north of Salt Lake City, and the broad area east of the Wahsatch, which 

 extends to the valley of the Weber. This latter Tertiary mass skirts the 

 whole east slope of the range, and west of Morgan Valley rises to a height 

 of 2,700 to 2,800 feet, resting unconformably against the eastern members 

 of the Farmington Archaean. Its position is from horizontal to a dip of 14° 

 to the eastward ; toward the base it is composed of beds of dark, brick-red 

 sandstone, but in rising passes into heavy conglomerates interstratified with 

 coarse sandstones. 



Farmington Arch^an Body. — West of this Tertiary region, and north 

 of the Laurentian Archaean body of Mill Creek, the whole Wahsatch, up 

 to the Weber River, is composed of a conformable series of westerly- 

 dipping Archaean schists. As far north as Farmington Caiion, the strike is 

 nearly with the range, i. e., about north 20° west; but, near the head of 

 Farmington Caiion, the strike bends rapidly to the east, and passes to 10° 

 east of north, which direction it keeps for about 4 miles, and then bends 

 around conformably with the trend of this part of the range, viz, 15° to 20° 

 west of north. In the axis of these two general flexures, the rocks are much 

 broken, and the dip very irregular. As a general thing, the whole of this 

 Archaean mass dips at about 15° to 20° to the west. There is, therefore, 

 exposed from 12,000 to 15,000 feet of these schists. 



The lowest exposed members are a great variety of mica and horn- 

 blendic gneisses and schists, together with a few granitoid beds and some 

 limited quartzites and slates. The main series is composed of a varying 

 family of gneisses; the lowest of these are very coarse, composed of large 

 crystalline masses of flesh-colored feldspar and partially-decomposed, earthy, 

 brown mica, and large milky-white, irregular bodies of quartz. This rock 

 is interesting, as showing the transition from an evenly-bedded rock into a 



