Annual report of the United States Geological Survey to the Secretary of the Interior . e layer 575 feet. The clastic series of the Mountain mine may be said to eud here, the entire thick-ness (Nos. 603-607 and 599) being approximately 700 feet. 10. Next east is No. 608. Quartz-porphyry tuff. The microscope shows this to beplainly clastic and to contain microlitic fragments, cryptocrystalliuo granular frag-ments (chert?), rounded volcanic quartzes, and fragments! feldspars. There areinterbedded with this material a few thin layers of siliceous argillite. 11. No. 609. Also a quartz-porphyry tuf
Annual report of the United States Geological Survey to the Secretary of the Interior . e layer 575 feet. The clastic series of the Mountain mine may be said to eud here, the entire thick-ness (Nos. 603-607 and 599) being approximately 700 feet. 10. Next east is No. 608. Quartz-porphyry tuff. The microscope shows this to beplainly clastic and to contain microlitic fragments, cryptocrystalliuo granular frag-ments (chert?), rounded volcanic quartzes, and fragments! feldspars. There areinterbedded with this material a few thin layers of siliceous argillite. 11. No. 609. Also a quartz-porphyry tuff and lies just east of layer 608, the thiok-ness of the two being perhaps 1,000 feet (approximate only). The general strike of the elastic beds of the Mountain mine and thequartz-porphyry tuffs lying just east is to the west of north, and the<lip, except in the crushed zone along the quartz vein, is uniformly tothe east at from 50° to 00°. Overlying the above beds are more even-grained greenstone tuffs(Nos. (HO to (!12), which may be called uralite-andesite tuffs, the original. TUEXER.] JURATRIAS BEDS. 623 augite being largely replaced by uralite, etc. This is plainly a morebasic series and does not, so far as examined, contain original freequartz. Although these massive tuffs exhibit planes or partingsparallel to the dip planes of the underlying sediments, no clear evi-dence of the dip of these beds was noted along the Mountain mineroad, where they are finely exposed. The uralite-andesite tuff bed con-tinues eastward (down the slope) for more than 3,000 feet, where theunderlying rock is obscured by morainal material. However, about 1mile farther south, in the bed of the North Fork of the North Fork ofthe Yuba River, this uralitic augite-feldspar tuff is plainly seen to beoverlain by the red slates and fine-grained tuffs of the Milton forma-tion. The same succession of the beds here indicated, from the quartz-porphyry to the Milton series, inclusive, is also to be seen on
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