METAJIOKI'IIOSKI) SANDSTONES. 143 



opjiortuuitx tnr rlic collectiitii of ;i DcvDiiian taiiiia. The tew hours spent 

 here gavt' jmnnise of an abundant harvest if time would permit of a dili- 

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

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

 bcinu- formed of the latter beds. 



Metamorphosed sandstones.— J nterstratified in the Xevatla limestone of this 

 ridge oecur numerous l)ands 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 occiuTing at varying intervals througliout nearly 1, ()()() feet of 

 limestones. 



Instances of sandstones in limestones are couininn enough ami woidd 

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

 considerable alteration, and as the original material was more or h'ss 

 impure, the\' have developed under dynamic influences a crystallization 

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

 but at the same time e.xhibit remarkable transitions from a normal sand- 

 stone to a rock closely resembling a cry ptocrystalliue granite. 1'he (piartz 

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

 seen in a conqiact sandstone made tip from the disintegrated material 

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

 of musct)vite with some ferrite and calcite. It is e\'ideut 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, vet the\ are 

 associated with others which have undergoneso gi'eat an alteration that thev 

 present many structural features of igneous rocks. The transition from 

 un(loul)te(l sanilstone to the liighlv metamorphosed l)eds shows every stage 

 of gradation and it is impossible not to see the close relation.ship existing 

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

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

 however, have undergone decomposition, and are accompanieil b\- calcite 

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

 talline bodies exjiosed along the west sides of Signal and 3I(tdoc peaks attain 



