METAMORPHOSED SANDSTONES. 143 



opportunity for the collection of a Devonian fauna. The few hours spent 

 here gave promise of an abundant harvest if time would permit of a dili- 

 gent search. From this shale belt the limestones pass down into the Lone 

 Mountain series, the hill lying between Brush Peak and Spanish Mountain 

 being formed of the latter beds. 



Metamorphosed sandstones. Interstratified in the Nevada limestone of this 

 ridge occur numerous bands of fine grained sandstones with their bedding 

 planes parallel to the inclosing rock. Some of them may be traced for over 

 a mile without interruption, rarely exceeding 50 feet in thickness, but most 

 of them only a few feet in width. They are shown in the section north of 

 Modoc Peak occurring at varying intervals throughout nearly 1,000 feet of 

 limestones. 



Instances of sandstones in limestones are common enough and would 

 call for no special comment but for the fact that here they have undergone 

 considerable alteration, and as the original material was more or less 

 impure, they have developed under dynamic influences a crystallization 

 and structure of a micro-granite. All of these sandstones show alteration, 

 but at the same time exhibit remarkable transitions from a normal sand- 

 stone to a rock closely resembling a cryptocrystalline granite. The quartz 

 grains are granitoid in structure, and do not show the action of water usually 

 seen in a compact sandstone made up from the disintegrated material 

 derived from an older rock. Accompanying these quartz grains are flakes 

 of muscovite with some ferrite and calcite. It is evident that the beds have 

 undergone a marked change since they were originally laid down. That 

 these rocks are of sedimentary origin no one would question, yet they are 

 associated with others which have undergone so great an alteration that they 

 present many structural features of igneous rocks. The transition from 

 undoubted sandstone to the highly metamorphosed beds shows every stage 

 of gradation and it is impossible not to see the close relationship existing 

 between them. In the more highly altered rocks may be observed well 

 developed feldspars, both orthoclase and plagioclase. Most of the feldspars, 

 however, have undergone decomposition, and are accompanied by calcite 

 and other secondary products. Singularly enough, some of the more crys- 

 talline bodies exposed along the west sides of Signal and .Modoc peaks attain 



