816 LLL JOO LIN AL OL) NGID OM O|GWe 
quartz phenocrysts. The micropoikilitic structure has been held 
in some cases to be of secondary origin.*. I can find, however, 
no evidence whatsoever which indicates a secondary origin for 
the structure in these rocks. On the other hand, there is like- 
Puate II. 
Fic. 2.—The same section in polarized light, showing the micropoikilitic zone 
around the quartz phenocrysts. The irregular small dark spots in the white network of 
quartz are the feldspar grains. Magnified 18 diameters. 
wise an absence of evidence proving unquestionably its primary 
character. Rather, however, than accept an explanation which 
*R. D. Invinc: The Copper-bearing Rocks of Lake Superior. Mon. V., U.S 
Gis Shp fb DOy W'S}, 
F. Bascom: Structures, Origin and Nomenclature of the Acid Volcanic Rocks of 
South Mountain. JOURN. OF GEOL., Vol. IL, No. 8, p. 816. Nov.—Dec., 1893. 
