226 EDWARD B. MATHEWS 
abundant and in smaller areas, and the numerous fine grains in 
the groundmass are free from much included matter. The 
larger individuals, however, present the broad zones of inclusions 
noticed in the preceding type. The porphyritic feldspar is 
microcline, as in the first INOS, IW: InEre ae perthitic inter- 
growths of albite are much less common. The microcline also 
Fic. 7.—Summit type fine grained granite-porphyry. 
composes much of the groundmass where it fills the interstices 
between the grains of quartz. Untwinned clear grains of feld- 
spar, probably orthoclase, are also present in the groundmass in 
considerable abundance. Oligoclase showing fine twinning 
lamellae is more poorly developed than in the Pikes Peak type. 
All of the feldspars are much clouded with alteration products, 
especially by sericite and some iron compound, either hematite or 
limonite. The abundant development of micropegmatitic inter- 
growths of quartz and microcline in this type is noteworthy, as 
these are practically wanting in the fresh Pikes Peak granite. The 
