674 DESCEIPTIVE GEOLOGY. 



water is found in abundance, nearly every large canon furnishing a con- 

 siderable stream, which is due partly to the width of the more elevated 

 regions, but, in part, to the great diversity of geological structure, with its 

 folded and crumpled strata inclined in various directions. Timber is scarce 

 even on the higher slopes. 



Large masses of granite, probably of Archaean age, represent the 

 oldest rocks of the Havallah Eange. These are directly overlaid either by 

 immense bodies of heavily-bedded quartzites, or else by still later beds of 

 limestone, with some intercalated beds of quartzite and sandstone ; the 

 entire series, which constitutes nearly all the higher portions of the mount- 

 ains, and forms a continuous body for 35 miles, being referred to the Trias- 

 sic age, as no Palaeozoic strata have been recognized west of the Battle 

 Mountains. Breaking through the granites and Mesozoic formations are 

 occasional narrow dikes of diorite, and still later, more extensive outbursts 

 of Tertiary volcanic rocks, represented by propylites, trachytes, rhyolites, 

 and basalts. 



The large granitic masses are confined to two distinct bodies, at the 

 northern end of the range, separated by a broad Quaternary depression, at 

 no point less than 3 miles wide, known as Eagan's Valley. On the east side 

 of this valley, the granite forms a bold ridge nearly 15 miles in length, but 

 barely more than 4 miles in width, with a trend approximately northeast 

 and southwest. It rises from 2,500 to 3,000 feet above the recent beds, 

 which surround its base, and is characterized by a broken serrated crest 

 with great diversity of outline, quite unlike most of the granitic bodies of 

 Central Nevada. To the northward, it falls away gradually, until concealed 

 beneath the Quaternary of the Humboldt Valley ; while to the southward 

 it descends to Summit Springs, scarcely 500 feet above the plain, where it is 

 overlaid by heavy sedimentary beds, which have been referred to the hori- 

 zon of the Star Peak group, and will be described further on. The springs 

 which give the name to the pass occur at the junction of the two formations. 



This granite has much the physical attitude of many of the Archaean 

 granitic bodies observed in the Colorado Eange of Colorado and Wyoming. 

 It is a structureless mass, without well-defined lines of bedding, of coarse- 

 grained rock, with a loose friable texture, crumbling readily into irregular- 



