FRACTION EXTENSION SHAFT. 201 



perhaps not at all, from the tuffs of the Fraction dacite breccia, which iu general 

 is considered to underlie the first named. In the shaft portions were passed 

 through which resemble the Tonopah rhyolite-dacite; these ma}' represent dikes, 

 especiall}' in the lower portion. As a whole, however, the shaft may be considered 

 to lie within the Fraction dacite breccia. 



The first 150 feet is rather fine volcanic breccia, followed by 275 feet of frag- 

 mental tuff, light-colored and generally moderately coarse. This is horizontally 

 coarsely stratified and contains one bed, 1 feet thick, of finely stratified fine-grained 

 material. This passes gradually into a fine breccia and this into a vecy coarse 

 breccia containing included fragments up to 2 or 3 feet iu diameter. Most of 

 these inclusions are various phases of the later andesite, but some are probably 

 earlier andesite. Others are of dacite and tuff, much like the matrix. At the 

 time of the writer's examination the shaft was 475 feet deep, and had passed 

 through 50 feet of this coarse breccia. Specimens obtained from the shaft during 

 its progress farther downward showed that it remained in practically the same 

 material, some of the included bowlders of earlier and of later andesite being 

 several feet thick. The bottom of the shaft is in soft dacite that contains later 

 andesite inclusions. This dacite is much like that which caps the Fraction shafts. 



The stratified tuffs referred to do not belong to the Siebert tuffs of the lake 

 beds, but are included in the Fraction dacite breccia. They are described else- 

 where as the interbreccia tuffs, and are found in the upper part of the Fraction 

 dacite breccia at various places in the district. The great thickness of the Fraction 

 dacite breccia, here shown, indicates that the block in which the New York Tonopah 

 lies has sunk down very considerably in respect to the blocks farther northeast 

 to those, for example, in which the Fraction shafts are situated. The breccias 

 and tuffs of the New York Tonopah are considered to be surface formations, formed 

 chiefly by explosive outbursts; and the included blocks of earlier rocks are con- 

 sidered to be fragments hurled out of the volcanoes at the time of the explosions. 



FRACTION EXTENSION SHAFT. 

 GEOLOGICAL SECTION'. 



This shaft is situated at the south base of Brougher Mountain, somewhat over 

 a thousand feet northwest of the New York Tonopah shaft. When visited by the 

 writer it was approximately 300 feet deep. On account of the tight lagging the 

 section of the shaft could not be observed, but a roughly estimated thickness of 75 

 or 80 feet of the white finely stratified tuffs of the lake beds was first passed 

 through. Below the tuffs the whole shaft is in hard gray or red brecciated lava, 

 belonging to the glass} 7 Tonopah rhyolite-dacite. 



