THE LOWER HURONIAN. 365 



DISTRIBUTION, EXPOSURES, AND TOPOGRAPHY. 



The granite is confined in its distribution to the immediate vicinity of 

 Cacaquabic Lake, and is especially well developed on the southern side. 

 It extends back from the lake for a maximum distance of about a mile, 

 reaching down into the SE. i of sees. 1 and 2, T. 64 N., R. 7 W. The 

 granite occupies on the whole higher ground than is occupied by the 

 adjacent rocks, forming, especially in sees. 1 and 2, fairly high hills. There 

 are excellent exposures on a number of islands in the lake and also on the 

 mainland near the shore. 



PETROGRAPHIC CHARACTERS. 



The Cacaquabic granite, like the other granite complexes of the Ver- 

 milion district, shows considerable variation both in texture and mineralogic 

 composition. The main mass of the granite is a medium-grained gra}' or 

 pink to red rock, whereas on the periphery of the granite area the finer- 

 grained and granite-porphyiy facies are developed. 



The granite-porphyry facies contains larg-e phenocrysts of plagioclase 

 feldspar lying in a fine-grained gray to red groundmass. The phenocrj^sts 

 themselves range from gray to red in color, depending on the degree and 

 the character of the alteration. When red in part or as a whole, the 

 phenocrysts give the granite-porphyry a very striking appearance. They 

 then stand out prominently from the lighter-colored groundmass. In general 

 there seemed to be no arrangement of the phenocrysts, but in one case the 

 phenocrysts of the granite-porphyiy did show a distinct parallelism of their 

 major dimensions. There was thus produced a more or less perfect 

 macroscopic flowage structure. 



The granite and granite-poi-phyry are massive, although in places 

 much jointed and separated into small blocks by the joint planes. In 

 places" the fractures in the granite are filled by veins of infiltrated quartz. 



Minei'alogically the granite varies considerably. While the main mass 

 is an augite-soda granite,'' an examination of the specimens collected shows 

 variations to a hornblende-granite and hornblende-mica-granite. Grant 

 reports an augite-biotite-syenite facies." The minerals constituting the 



«The Geology of Kekekabic Lake, by U. S. Grant: Geol. and Nat. Hist. Survey of Minnesota, 

 Twenty-first Ann. Rept., 1892, pp. 34-36. 

 ''Loc. cit, p. 33. 

 cLoc. cit., p. 50. 



