REGION NOETH OF GEANITE MOUNTAIN. 709 



tions in the Havallah Range. But it should be stated that between the 

 qiiartzites of the Havallah, Pah-Ute, and Humboldt Ranges, there is too 

 much similarity in structure and position not to believe that they belong to 

 one and the same geological horizon ; and, in the latter range, the Koipato 

 and Star Peak beds are clearly conformable. 



East of the quartzite formation there occurs an immense outburst of 

 basalt, which extends in a north and south direction for 15 miles, forming the 

 more elevated portion of the range. It rises nearly 3,600 feet above the plain, 

 falling off gently eastward in broad table-like ridges, which stretch across 

 Grass Valley nearly to the Havallah Range. Several measurements of the 

 angle of the basaltic flow were made, varying from 3^° to 8^*^, the average 

 inclination being 5°. This heavy basaltic mass is cut in a number of 

 places by deep canons, which offer good exposures of the flows, showing a 

 uniform mass of dark compact dolerite of normal composition. Outcrops 

 of limestone are said to occur along the west base of the basalt, lying 

 between it and the quartzite. 



The relation of the basaltic field to the underlying quartzite and its 

 position in the depression between the main uplifts of the Pali-Ute and Ha- 

 vallah Ranges is shown in the upper geological section at the base of Map 

 V. North of the basalt, the granite body already described comes in, where 

 it appears to form a barrier to the extension of the volcanic eruptions in that 

 direction ; but m the caiion coming down from Spaulding's Pass, and lying 

 between the two larger rock-masses, is a small body of fine-grained compact 

 diorite not unlike some of the occurrences in the south. 



Resting directly against the granite body on the west occur the Star 

 Peak Triassic beds, which encircle around its mass to the northwest. Next 

 to the granite are found heavy beds of blue limestone, highly crystalline 

 and metamorphorsed, in places almost changed into marble, standing at a 

 steep angle, and forming both walls of Upper Willow Canon, which here has 

 approximately a north and south course. These strata underlie conforma- 

 bly the great series of beds that are well exposed throughout the entire 

 length of Inskip Canon, dipping always to the westward, but at very vary- 

 ing angles. They consist of quartzites, limestones, and some interstratified 

 slates, passing up near the entrance to the caiion into thinly-bedded slates, 



