PROPYLITBS OF THE FORTIETH PARALLEL. 135 



crystals are as large as the olivines, but while there are many small augites 

 there seem to be no microscopic olivines The augites are better crystal- 

 lized than the olivine, and often show characteristic sections and cleavages. 

 They are decidedly dichroitic. The augites carry a few bul)ble-bearing 

 inclusions, which seem to be glass. The feldspars are small, lath-like, and 

 often simply twinned. In a very few cases both periclinic and albite twin- 

 ning are visible. The angles of extinction are those of labradorite. I could 

 detect no orthoclase. The groundmass consists of feldspar, augite, and 

 magnetite in cubes, and contains no perceptible base. Slide 458 from 1,250 

 feet southeast of Roux's Ranch is identical with the above, and with the slide 

 described in the Exploration of the Fortieth Parallel, Vol. VI., as 528. The 

 shde and specimen described in that memoir as 529 is the same rock which 

 is here regarded as a metamorphie diorite. 



PROPYLITES OF THE FORTIETH PARALLEL SURVEY COLLECTION. 



Fortieth Parallel propyiites.— I luive bceu kludly allowed frec use of the collec- 

 tions of the Geological Exploration of the Fortieth Parallel, and reproduce 

 in the following pages my notes on the specimens and sHdes described in 

 Vol. VI. of the publications of that survey as propyiites (212 to 225) and 

 as quartz-propyhtes (226 to 232). While I do not feel myself competent 

 to decide definitively the species of those rocks which I have not had an 

 opportunity of studying in the field, my opinion of each slide is indicated, 

 in order to convey a more complete impression of its appearance. 



Exploration of the Fortieth ParalleL Slide No. 212, specimen No. 22,682, Crown Point 



Ravine, Washoe. 



This is a smooth, fine-grained rock, somewhat resembling a limestone 

 in texture. Its color is pistachio green. Seen under the microscope, it is 

 evidently much decomposed; indeed, the slide shows little besides epidote 

 and secondary quartz. Even the magnetite has almost wholly disappeared, 

 and the residual products are grouped within no outlines from which the 

 nature of the original bisilicates might be inferred Many very small feld- 

 spars are still fresh enough to make out with certainty that they are triclinic. 



