PENNSYLVANIA HILL. 135 



the Sacramento type, occurring as it does in geographically debatable 

 ground, or about at the limits of the extent of either variety. They occur 

 in the lower part of the Cambrian, the .upper sheet being 30 feet thick on the 

 line of the section, above which is a long dike about three feet thick, proba- 

 bly an offshoot from it. The lower sheet, which on this line has a thin bed 

 of quartzite included in its mass, is 15 feet thick, and is found a little farther 

 west without any included quartzite. This lower porphyry sheet extends 

 westward along the north face of Pennsylvania Hill as far as the London 

 fault. 



Pennsylvania Hiii. This name has been given to the broad, flat-backed 

 spur included between Mosquito and Big Sacramento gulches. Like its 

 neighbor, Loveland Hill, it is the locus of a slight synclinal fold, which 

 forms a shallow ravine on its back drained by Pennsylvania Creek Except- 

 ing along the cliff walls of the adjoining canons, it affords but few good rock 

 exposures, since its surface and that of the spurs which run down from it 

 to the valley of the Platte are densely covered with forest growth and soil. 

 The varying direction of dips observed in the sandstones of the Weber 

 Grits which form the lower spurs gives evidence of one or more secondary 

 rolls or folds in the outlying strata, as indicated in somewhat generalized 

 form on Sections D and E, Atlas Sheets VIII and IX. The most definite 

 evidence is found on the hill south of Park City, known to the miners as 

 Baldhead. The northeast slopes of the hill and many of the lower hills 

 extending eastward from it are made up of moraine material from the ancient 

 Mosquito glacier. The various porphyry bodies found in this wooded re- 

 gion, of which only the more prominent are indicated on the map, are gen- 

 erally very much decomposed. When their character could be still recog- 

 nized they were found to belong to the Sacramento type. They have gen- 

 erally a greenish color, due to the peculiar alteration of the basic constitu- 

 ents of the rock. Above timber-line the slope of the hill corresponds so closely 

 with that of the stratification planes that good outcrops are only to be found, 

 as a rule, on the cliff faces to the north, west, and south. The shallow ravine 

 on its back divides it into two portions, on the northern of which the beds 

 have the prevailing strike already observed, viz, about north and south. On 

 the southern portion, on the other hand, the strike is about 20 west of north, 



