464 



A, F. BUDDINGTON 



orthoclase, with quartz and magnetite in the acid tuffs, and of 

 plagioclase, augite, magnetite, apatite, and foreign crystals in the 

 basic tuffs. Some of the basic tuffs resemble typical palagonite 

 tuffs (Fig. 10). 



The lithic tuffs consist predominantly of fragments of rhyolite 

 or of pilotaxitic basalt, according to their nature, in a groundmass 





V-- 



K ^ 



Fig. 10. — Groundmass of basaltic crystal tuff, with devitrified shards of glass 

 bordered by rims of fibrous, brownish material. Hill 937 near Holyrood. Micro- 

 photograph. Natural Hght. 



consisting of finely comminuted materials similar to the lithic 

 fragments, with crystals of feldspar and quartz in minor amount. 

 The volcanic-dust beds are frequently well bedded and chertHke 

 in character, often translucent in thin edges, with a conchoidal to 

 subconchoidal fracture. 



The waterworn volcanics comprise volcanic conglomerates, 

 sandstone, and a rare red shale bed. The prevalence of volcanic 



