38 SYDNEY H. BALL - 



the post- Jurassic igneous intrusives. But when we consider only 

 the region at present covered by pre-Tertiary formations we find 

 that the widely distributed masses of post- Jurassic igneous rocks 

 form approximately one-sixth of this territory. Moreover, at many 

 places where Tertiary lavas mask the older formations, fragments 

 of pre-Tertiary igneous rocks are included in the lavas, thus showing 

 the presence of these older rocks on the sides of the conduit through 

 which the molten Tertiary rock welled. 



THE GRANULAR SILICEOUS SERIES 

 GENERAL STATEMENT 



This series is composed of four rocks which were intruded in the 

 following order; monzonite and quartz-monzonite porphyry; granular 

 rocks, including granite, quartz-monzonite, and soda syenite; aphtes 

 and pegmatites. These rocks in each separate bathoHth soHdified 

 successively from a single magma in the reverse order of their acidity. 



MONZONITE AND QUARTZ-MONZONITE PORPHYRY 



The granular igneous rocks of the Belted and Panamint ranges, 

 of Pahute Mesa, and of Gold Mountain Ridge, contain fragments of 

 fine-grained gray monzonitic rocks. That of Gold Mountain is a 

 quartz-monzonite porphyry in which the ferromagnesian mineral is 

 biotite. A specimen from the Belted Range is a basic hornblende- 

 biotite-monzonite. These monzonites, while somewhat older than 

 the granular sihceous rocks in which they occur, are massive and are 

 beheved to be a somewhat earlier crystalHzation of the magma from 

 which the more sihceous rocks afterward sohdified. 



GRANITES, QUARTZ-MONZONITE AND SODA-SYENITE 



Petrographic character. — These rocks range on the one hand from 

 alaskite through muscovite-, muscovite-biotite-, and biotite-granite to a 

 quartz-monzonite approaching granodiorite, and on the other hand 

 from normal granite through soda-rich granite to soda-syenite. 

 Most of these rocks grade into corresponding porphyries. The 

 lithologic character of the rocks of most of the areas shown on the 

 map (see Fig. i) is usually rather constant, although in the Gold 

 Mountain Ridge granite-porphyry grades into hornblende-bearing 

 quartz-monzonite porphyry in a distance of only ten feet. 



Many of these rocks are characterized by large porphyritic feld- 



