UTAH PROPYLITES. 143 



cite, and it strikes me as possibly iron carbonate. The quartz is indis- 

 tinctly separated from the groundmass, and seems to me secondary. The 

 feldspars and the groundmass have the usual characters of Washoe horn- 

 blende-andesites 



Exploration of the Fortieth Parallel. Slide No. L'32. 



By some mistake this slide was labeled as from Berkshire Canon, 

 whereas the check-list of the survey, no less than the correspondence of 

 the slide and specimen, show that it should have been numbered 155, and 

 that the rock is the typical diorite of Mount Davidson, in Washoe. The 

 descriptions of this rock and of the Mount Davidson diorite, like the slides, 

 asrree. 



PKOPYLITES OF THE GEOGRAPHICAL AND GEOLOGICAL SURVEY OF THE ROCKY 



MOUNTAIN REGION. 



Utah propyiites. — Captain Duttou lias also kindly furnished me with speci- 

 mens and sHdes of the propyiites mentioned by him in his memoir on "The 

 High Plateaus of Southern Utah." 



Geology of the High Plateaus of Utah. Slide and specimen No. 326. Base of Mount 

 Duttou, Sevier Plateau. 



Macroscopically a greenish, granular rock, in which lath-like feldspars 

 are separated out in a groundmass of a somewhat waxy luster. Under the 

 microscope it is seen that the rock is greatly decomposed, but also that in 

 a fresh state it consisted of plagioclase and augite, with an iron ore, quartz, 

 and apatite as subordinate constituents. A few of the augites are fresh, and 

 are in every way characteristic, but most of them have been converted into 

 chlorite, and the slide contains a large number of excellent pseudomorphs of 

 this character. The chlorite appears to be precisely the same as that to which 

 reference has been made so often in the foregoing pages. It is fibrous, ex- 

 tinguishes light parallel to the long axis of the microlites, dichroizes strongly, 

 and gives an aggregate polarization or a spherolitic cross, according to the 

 arrangement of the microlites. In places epidote may be seen forming at 



