006 DESCRIPTIVE GEOLOGY. 



Maggie's Peak is made up of a granite similar to that of Nannie's 

 Peak, but having a still more porphyritic texture. It has the same tend- 

 ency to weather into thin slabs as that of Nannie's Peak. It is a gray, 

 rather fine-grained rock composed of mica and hornblende, and relatively 

 little quartz, with both monoclinic and triclinic feldspars. This rock has been 

 classed by Zirkel as granite-porphyry. It is associated with a well-defined 

 felsite porphyry, which closely resembles a rhyolite in physical habit, 

 having the same tendency to separate into thin slabs, but carried to a 

 much greater extent than in the granite. In a white homogeneous ground- 

 mass, it shows few crystals besides those of quartz, but under the micro- 

 scope its gi'oundmass is seen to be entirely crystalline, and the quartz to 

 abound in fluid-inclusions, sufiicient guarantees of its earlier origin. The 

 rhy elites adjoining this porphyry, from which in the field it can be with 

 difficulty distinguished, are whitish and red compact rocks, containing like- 

 wise only crystals of quartz. The exposed surfaces present beautiful botry- 

 oidal secretions of hyalite and opaline chalcedony. 



At the extreme southwestern point of the range is a body of gi'ay sili- 

 ceous limestone, forming an outlying ridge, through which Maggie Creek 

 has cut a narrov*^ caiaon. As far as observed, it was entirely barren of fos- 

 sils, and, on account of its isolated position, no evidence was obtained as 

 to its geological horizon. It has, however, been assigned, on general 

 grounds, to the Lower Coal-Measure group. 



The valley of Maggie Creek, like that of Susan Creek, is covered by white 

 Pliocene beds. At the head of the valley, the low divide between it and that 

 of the North Fork of the Humboldt is occupied by various flows of rhyolites, 

 some white earthy varieties and some dark obsidian-like pearlites containing 

 white feldspar crystals. To the north of this divide, the range is continued 

 by a higher ridge, en echelon with the Nannie's Peak Ridge, which forms the 

 eastern boundary of Independence Valley, and stretches northward beyond 

 the limits of the map in a high important mountain mass. 



This portion of the Seetoya Mountains is made up of heavy bodies of 

 quartzite, which have been considered to represent the Weber Quartzite in 

 this region, inasmuch as they are both underlaid and overlaid by lime- 

 stones. The structure of the ridge is that of an anticlinal fold, whose axis 



