AUGUSTA MOUNTAINS. 657 



erate, formed of greenish, clierty pebbles, in a reddish matrix, like the con- 

 glomerates of the New Pass Mountains, which would indicate the existence 

 of the Star Peak Triassic body here, and that the anticlinal axis of the fold 

 sinks to the northward. Some of the beds of limestone are very rich in 

 fossils, but the rock is so much metamorphosed that it was very difficult to 

 obtain good impressions. The lithological character of the limestone closely 

 resembles that of the New Pass Mountains, but the fossils have a decidedly 

 younger aspect, and have been assigned to the Jurassic horizon. Some of 

 the forms have a facies which allies them to the Cretaceous or even to 

 Eocene Tertiary formations ; but the position and lithological character of 

 the beds, and the fact that no Cretaceous or Eocene Tertiary beds have been 

 found in this region of Western Nevada, preclude the possibility of their 

 representing a later formation than the Jurassic. The following forms 

 were determined by Messrs. Hall and Whitfield : 



Terebratula Augusta, n. sp. 



Septocardia Carditoidea, n. sp. 



Septocardia typica, n. sp. 



Aviculopecten {Eumicrotis f) Augustensis, n. sp. 



Fecten, sp.? 



Pecten, sp.? 



GrypJicea, sp.? 



Discina, sp.? • 



In a little ravine between the limestone hills was found a small out- 

 crop, only a few feet in extent, of a curious rock, made up mostly of horn- 

 blende and quartz, with a little feldspar. The hornblende is extremely 

 cleavable, and has somewhat of a parallel arrangement, which gives the 

 rock at first sight the appearance of an Archaean schist. To the north of 

 this point, under the rhyolite hills which bound Soldier's Spring Valley, 

 on the west, are found considerable outcrops of a similar rock, much more 

 decomposed, however, which was first taken for a syenite. A micro- 

 scopical examination, however, shows that among the feldspars plagioclase 

 decidedly prevails, and that the rock therefore belongs rather to the diorites. 



It is a rather coarse-grained diorite, and contains, besides hornblende and 

 42 D G 



