248 IRVING. 



They consist of meta-diabases and meta-gabbros whose chief 

 components are plagioclase feldspar, hornblende of the variety 

 iwalite and accessory ilmenite, calcite, apatite and quartz. 

 Cores of large dikes show uralite masses with augite kernels, 

 furnishing a clue to the original character of the rock. Such 

 cores pass towards the periphery with increasing schistosity, 

 proceeding by insensible gradations into chlorite and hornblende 

 schist. 



DETAILED DESCRIPTION. 

 I. Quartz-segrite-porphyry. 



This rock is of an exceedingly interesting character as it 

 corresponds exactly in some cases to rocks in Norway, de- 

 scribed by W. C. Broegger, as Groriiditc. In their general ap- 

 pearance these rocks are massive and homogeneous. They 

 range in color from a light greenish gray to almost a white in 

 the more coarse grained and porphyritic varieties. The texture 

 varies from almost completely aphanitic, through porphyritic up 

 to one almost granitoid. In some varieties the quartz cannot 

 be observed in the field, but two very interesting occurrences 

 exhibit very large and numerous phenocrysts of quartz, which 

 have led previous observers to class them with the rhyolites. 



The quartz-aegirite-porphyries will be described under the 

 following types : 



1. Lost Camp Creek type. 



2. Elk Mountain type. 



3. Terry Peak type. 



4. Annie Creek type. 



5. Sunset Mine type. 



6. Bald Mountain type. 



I. Lost Camp Creek Type. 



Megascopic Appearance. — As seen in the field this rock is a 

 light greenish gray and is very fine-grained. The phenocrysts 

 consist of orthoclase, in sparsely scattered crystals, and of very 

 small aegirines which may be seen distributed through the rock. 



