DIOEITES OF ELECTRIC PEAK. 101 



coarser-grained varieties. The border is allotriomorphic and more alkaline 

 than the center. Orthoclase is recognizable in the coarsest-grained rocks. 



Quartz occurs in allotriomorphic crystals, nearly contemporaneous with 

 the orthoclase, which is also allotriomorphic. The gas and fluid inclusions 

 in the quartz increase in number and in size with the size of the quartzes 

 and with the grain of the rock. 



Hypersthene and augite form idiomorphic and allotriomorphic indi- 

 viduals in the porphyries. They are much more irregularly shaped in the 

 coarsest-grained rocks, and are in larger individuals. When grown together, 

 the hypersthene is always the older, being inclosed by the augite; rarely 

 they mutually penetrate one another, as though their crystallization was 

 synchronous. 



Primary brownish-green hornblende occurs in a similar manner. It fre- 

 quently surrounds the pyroxenes more or less completely, and is usually the 

 younger growth. Occasionally it appears to be contemporaneous with augite. 

 It is more abundant as the grain of the rock becomes coarser. Dark-brown 

 hornblende sometimes is present as an indejjendent crystallization. 



Biotite is mostly in allotriomorphic crystals. The ferromagnesian min- 

 erals occur isolated from one another to some extent, but are generally inter- 

 grown in the most intimate manner. Though there is an apparent order in 

 the time of their crystallization, beginning with hypersthene and augite and 

 ending with biotite, still in most cases they have grown synchronously. 

 This is specially true in the coarser-grained rocks. 



Magnetite has two periods of crystallization in the porphyritic rocks, but 

 only one in the uniformly granular ones, the size of the crystals increasing 

 and their number diminishing. Apatite forms abundant minute idiomorphic 

 crystals in the finer-grained rocks, and fewer, larger, poorly shaped indi- 

 viduals in the coarser-grained rocks. Zircon is more noticeable in the 

 coarser rocks and is in larger crystals. 



All of these variations of character plainly indicate that the physical 

 conditions that brought about the variation in the texture of the rocks 

 affected the crystallization of the earliest-forming minerals, and since these 

 conditions were localized in the stock, it follows that portions of the igneous 

 magma were completely liquid when they arrived in this part of the conduit. 



The intergrowths of green hornblende with pyroxene, which are the 

 results of primary crystallization in these diorites, find their analogies in 



