COETEZ AND PAPPOOSE PEAK REGION. 579 



overflow the eastern boundary of the quartz-propylite mass. The rock is 

 liere, as at the head of Agate Pass, a very fine, green, more or less globu- 

 litic dolerite. All this portion of the range is very much steeper on the 

 northwest side, where the older rocks are found, than on the southeast, 

 where the subsequent flows of volcanic rocks occur. 



With the granite, all the older rocks give out, and the range from 

 G-ranite Canon north to beyond the Humboldt River is entirely made up of 

 eruptive rocks. Skirting the northern edge of the granite outcrop, and 

 overflowing the northern extremity of the quartz-propylite, is a considerable 

 field of rhyolite, which occupies the summit and north slopes of the range, 

 and is deeply cut by sharp narrow canons, which expose fine sections. 

 These rhyolites, according to Zirkel,^ are distinguished from the others in. 

 the collection in the following points : " Their feldspars are, for the most 

 part, altered into a dull, half-kaolinic substance; they lack evidence of 

 any tendency to develop fibrous sphserolitic or axiolitic aggregations ; their 

 groundmasses, which are in a very imperfect crystalline state, and are rich 

 in ferrite, contain colorless feldspar-microlites, and they are absolutely free 

 from biotite. Most of the rocks from this locality are rich in quartz, which 

 is very pure, including only narrow lines of empty pores and beautiful iso- 

 lated glass-inclusions." 



In general appearance, the rock is of a bufi*, green, and purple color, 

 and largely made up of a breccia, of which the fragments are apple- 

 green, consisting of a very fine-grained, felsitic groundmass, containing a 

 few decomposed feldspars and numerous large angular and rounded 

 grains of quartz. These rounded grains of quartz are very peculiar, 

 and possess the characteristic botryoidal surface of hyalite or chalce- 

 dony. The pellets are sometimes as large as a small pea. The paste in 

 which these fragments of green rhyolites are imbedded is a rhyolite rich 

 in kaolinized feldspars and angular grains of quartz, which are sometimes 

 dihexahedral, and sometimes simply angular fragments. They are all sur- 

 rounded by a fine glazing, so that the cavities out of which the quartz- 

 grains fall present a smooth, pearly surface. It is noticeable that there are 

 also in the purple paste rounded quartz pellets, like those in the green frag- 



* Microscoi)ical Petrography, vol. vi, 194. 



