SILVERADO HILLS. 149 



ted to their search, but it seems hardly possible that they are absent, as occa- 

 sional evidence of poorly preserved corals was noted in the purer limestones. 

 Silverado Hiiis. South of Dome Mountain the Lone Mountain strata again 

 come in along the Pinto fault, and with the exception of occasional breaks 

 caused by overflows of both rhyolite and basalt continue to form the base 

 of the sedimentary beds until the ridges pass beneath the deposits of Fish 

 Creek Valley. These rhy elites and pumices, with the glassy basalts break- 

 ing through them, present identical features with those found in the basin 

 south of Richmond Mountain, while the basalts in the limestone do not 

 differ essentially from those occurring as dikes in pyroxene-andesite. 



The drainage from the slope of Hoosac Mountain follows a southeast 

 course until it meets the upturned Silurian ridge on the east side of the 

 Pinto fault, then runs south across the Pinto Basin, where, instead of con- 

 tinuing southward following the natural grade along the line of the fault 

 and across the soft, easily eroded pumices, it turns abruptly and follows a 

 deep channel cut clear through the hard rocks of English Mountain, finally 

 running southward to Fish Creek Valley. The divide between this water 

 course and the broad drainage channel running southward along the Pinto 

 fault and also emptying into Fish Creek Valley, lies only a few feet above 

 the level of the two stream beds. So far as can be made out the barrier 

 between the streams is wholly formed of recent lavas. It is similar to the 

 case mentioned in describing the drainage of Secret Canyon, where the 

 stream, after following the course of the canyon for a long distance, sud- 

 denly crosses the upturned ridge of Cambrian and Silurian rocks, avoiding 

 the low and insignificant ridge of volcanic material which blocks the 

 entrance to the canyon. The cause of this sudden turn in the course of 

 these stream beds is difficult to understand, but it is worthy of note that the 

 drainage channel bi-eaking through English Mountain lies nearly due east 

 of the one cutting Hamburg Ridge. 



The Lone Mountain beds are not so uniformly made up of limestones 

 as the corresponding horizon elsewhere. Many of the intercalated strata 

 resemble the underlying Eureka quartzites, but, as the latter nowhere carry 

 any considerable layers of calcareous material, siu-h a reference is out of 

 the question. That they correspond to the Lone Mountain horizon there 



