EMPIRE GULCH. 181 



Paleozoic beds. At the foot of the steep slope, between the Lower Quartz- 

 ite and the White Limestone, is a small body of eruptive rock whose out- 

 crops are so obscure that its structural relations could not be accurately 

 determined. It is a fine-grained, nearly white rock, with minute specks of 

 biotite and small white feldspars macroscopically visible as porphyritic 

 constituents. Microscopical and chemical examinations show it to be an 

 orthoclastic rock, containing 68 per cent, of silica. Glass inclusions occur 

 in both quartz and feldspar, but no fluid inclusions. It has been classed as 

 a rhyolite and is chiefly interesting on account of its isolated occurrence 

 and want of resemblance to any other rocks found in the region. 



Empire gulch. Empire gulch is one of the glacier-carved valleys of the 

 western slope of the range. At its head is a grand amphitheater cut out of 

 granite and gneiss, with a rim of sedimentary strata and intrusive porphyry 

 sheets crowning its wall. Two faults theoretically cross its upper portion 

 the Sheridan fault and the Mosquito fault which, however, are not visi- 

 ble in its Archean bed, as there is no distinction in the character of the 

 rock on either side to mark their position. At the Weston fault, however, 

 the Lower Quartzite occurs in the bed of the gulch, with an eastern dip, 

 and its outcrops sweep up the wall on either side ; these outcrops are par- 

 tially masked by two very well defined lateral moraines which border the 

 immediate bottom of the valley. 



On the south side of the gulch, in the basin inclosed by the north arm of 

 Empire Hill, is a shallow glacier lake, dammed up by one of these moraines. 

 In this basin prospect holes prove the existence of black shales and overlying 

 Weber Grits above the lake, while below it is the Blue Limestone, succeeded 

 by the White Limestone and Lower Quartzite, the line of the Union fault 

 being marked by the sudden appearance of White Porphyry, which adjoins 

 either of these two formations. Above the White Porphyry, on the steep 

 slope at the north point of Empire Hill, immediately west of the fault, is a 

 little remnant of Weber Shale. 



The moraine ridges terminate about a mile below (his north point of 

 Empire Hill. Here the valley of Empire gulch opens out into a broad al- 

 luvial meadow, below which it is cut mainly out of Quaternary Lake beds, 



