254 



IRVING. 



be caused by the parallel arrangement of a mass of feldspar in- 

 clusions, most of them orthoclase, but one or two of them 

 albite. (Fig. 13.) 



Fig. 13. Zonally arranged inclusions in quartz phenocryst from quartz-aegirite- 

 porphyry ; Annie creek type. 



5. Sunset Mine Type. 



This rock is perhaps the most interesting of the series. 



Megascopic Appearance. — It is a porphyritic rock, dark 

 colored in the fresher specimens, and shows large phenocrysts 

 of orthoclase and quartz. The quartz crystals are large, often 

 y% inch in diameter, and much rounded by resorption, and are 

 in many cases elongated ; sometimes so much so, that the 

 length will be fifteen times the breadth. When drawn out in 

 this manner, the phenocrysts all lie with their longer axes in the 

 same direction. 



Microscopic CJiaractcrs. — The feldspars are orthoclase, fre- 

 quently fractured and much resorbed. The cores of the crys- 

 tals are quite clear but the borders contain inclusions, and 

 seem to have been formed later than the main body of the crys- 

 tals. 



