PEOPTLITES OF THE FORTIETH PARALLEL. 139 



Exploration of the Fortieth Parallel. Slide No. 221", specimen No. 21,950. Between 

 the Truckee and Mouteziiina Ranges. 



The specimen strongly resembles those from the head of Ophir Ravine, 

 Washoe. It is highly decomposed, but the bisilicates appear to have been 

 hornblende. The feldspars have not the sharp outlines usual in andesites, 

 and the toute ensemble is that of a porphyritic diorite. 



Exploration of the Fortieth Parallel. Slide No. 222, specimen No. 21,542. Storm 

 Canon, Fish Creek Mountains. 



This is a ratlier coai'se-grained greenish rock, in which lath-like feld- 

 spars show 25rominently in a finer groundmass. The slide contains an 

 abundance of augites, some of which show pinacoidal cleavages as well as 

 the prismatic ones. The cleavages are very heavily marked. A portion of 

 the augite has been converted into grayish-green uralite, distinctly retaining 

 the crystal form of augite. Where it is favorably oriented it gives angles 

 of extinction of about 15°. The greater part of the augite has degen- 

 erated into chlorite, with the usual structure and optical properties. The 

 slide further contains much fresh mica, some of the scales of which are 

 horizontally placed, and give the biotite interference figure. There is also 

 a very little brown and intensely dichroitic hornblende, but I could find 

 none of this mineral which was green, except the uralite. The larger 

 plagioclases are well developed in lath-like crystals, but are nearly opaque 

 in consequence of the presence of decomposition products. The iron ore 

 occurs in irregular masses, but its nature is uncertain. The groundmass is 

 granular, not composed of well-developed microlites, but thoroughly crys- 

 talline. It contains much epidote and chlorite. 



Exploration of the Fortieth Parallel. Slide No. 22.3, specimen No. 21,545. Storm 

 Caiion, Fish Creek Mountains. 



This is the same rock as the last, but in a different stage of decompo- 

 sition. The green hornblende shows in numerous cases the cr^'stal outlines 

 of augite, and in my opinion is exclusively uralite. The plagioclases are 

 fresher than in the other slide and contain rounded fluid inclusions of small 

 size. While it may be somewhat rash to decide upon the age of this rock 



