472 PROCEEDINGS OP BALTIMORE MEETING. 



allanite. The rock, then, is the granitite of Rosenbusch, the biotite-granite of 

 Zirkel, and the true granite of Michel-Levy. 



Types 



NUMBER AND GROUPING 



Sixteen different types were separated in the field, which later study shows may 

 be collected into four groups, each of which will be described in a few" words. 



PIKES PEAK TYPE 



This variety is light grayish pink, weathering into bowlders or surfaces covered 

 by a hard silicious coating similar to " desert- varnish." The grain is medium to 

 coarse, the size of the individuals varying from several inches in length, in the 

 porphyritic variety from Raspberry mountain, to a quarter or half an inch in the 

 even grained masses typical of the entire area. In this we have a granite of coarse 

 individuals varying from a perfectly isomerous mixture to the distinctly porphyritic, 

 in which the phenocrysts may reach the length of six inches or more. 



SUMMIT TYPE 



This variety is confined almost exclusively to the Peak proper and its immediate 

 surroundings, though locally present in other areas. Its color is variably reddish, 

 purplish to light gray. When fresh it usually has a pinkish white tone, but when 

 weathered the rock presents a silver gray groundmass in which are outlined grayish 

 white feldspar phenocrysts. 



CRIPPLE CREEK TYPE 



This granite varies in color from a grayish white to a dark, almost black tone, 

 though its usual character is a bright though not brilliant red. The grain is medium 

 to fine, the texture saccharoidal-panidiomorphic. Tliis latter results from the charr 

 acter of the microcline, which occurs in rather short, chunky, twinned individuals 

 whose terminations are less clearly defined than the pinacoidal faces parallel to c^. 



FINE GRAINED TYPE 



This type is an isomerous, fine grained, granular rock in which none of the con- 

 stituents show a tendency toward a porphyritic development 



Genetic Sequence 



After the solidification of the main mass (made up of the Pikes Peak type), how 

 long we do not know, it was rent, especially in the area of the present peak, by 

 fissures which were filled immediately by a granite which crystallized into a fine 

 grained porphyritic rock of two varieties (Summit type), the one having pheno- 

 crysts which still retain a fresh almost glassy appearance, the other finer grained 

 and bearing smaller more or less opaque feldspar phenocrysts. As the last product 

 in the formation of this granite mass, its newly formed fine fissures were filled by a 

 fine grained red granite. This granitic injection was accompanied sometimes by 

 a development of quartz-feldspar pegmatitic veins. 



When the last feature in the formation of the entire granitic mass took place we 

 do not know. There must have been, however, a considerable lapse of time be- 



