CENTEAL AKD EASTEEN NEVADA. 327 



To subsequent metamorpliic or eruptive action is probably due the form- 

 ation of tbe numerous veins and dikes which intersect the original formations. 

 The intensity of metamorphic action has increased toward the south, as seen 

 in the metamorphic granite at Ophir Canon, and the partially crystalline slates, 

 which, at the Twin River, are replaced by metamorphic diorites. There are 

 also evidences of later dynamic action, whose extent cannot be determined. 



In the volcanic period the appearance of the propylite bodies of the 

 Point of Rocks was accompanied by considerable disturbance of the adjoining 

 rocks, which now seem to rest upon it, and to be somewhat altered at the 

 contact; this action was apparently more extensive to the south than to the 

 north of this body. The southern eruption of propylite seems to form a con- 

 tinuation of the western Ophir Canon body of granite to the south, covering 

 the present bed of the Twin River basins, and to have been accompanied by 

 extensive metamorphic action on the rocks to the east of it. 



The rhyolite eruptions have not in general been accompanied by any 

 considerable disturbance or alteration of the adjoining rocks. Those of 

 Mount Poston, and the peaks above the Hot Springs, have overflowed the 

 propylite and, probably, the slates of the western slopes of the range; it is 

 not certainly known whether the San Juan rhyolite is part of this flow or an 

 independent eruption; the indications of a lateral fold in the strata here would 

 favor the latter supposition. The rhyolites at the mouths of Big Creek and 

 Kingston are small isolated outflows, which have apparently had no action 

 upon the adjoining rocks. The Mount Prometheus rhyolite has broken 

 through granite, overflowing its flanks and those of the slates which rest 

 upon it. 



The sections given on Plate XXVI, which present approximate pro- 

 files of the range at difierent points, will serve to illustrate the idea intended 

 to be conveyed in the above description. 



No. 1, on a line drawn through Mount Prometheus, east 13° south, 

 shows the relations of the granite and rhyolite bodies at that point. 



No. 2, on a line drawn through Globe and Big Creek Peaks, east 6° 

 south, shows the main antichnal fold, though it cannot serve for an accurate 

 representation of the thickness of the strata, since their strikes vary so much 

 that it is impossible to choose a line which shall cut them at right angles. 



