Plate i8 



Photomicrographs by \V. J. Miller 



Upper left figure. Part of slice of gabbro from dike no. 5, one-half of 

 a mile south-southwest of Owen pond. Shows very fine diabasic texture. 

 Toward top, a large phenocryst of olivine with a thin rim of magnetite or 

 ilmenite. Dark gray angular patches, brown augite ; black patches, magnetite 

 or ilmenite; white material, plagioclase. Ordinary light. Magnified 23 

 diameters. 



Upper right figure. Part of slice of diabase from quarry at southern 

 base of Hamlin mountain. Toward top, augite phenocryst with inclusions 

 black patches) of pyrite. White laths are labradorite crystals embedded in 

 a black glassy groundmass. Ordinary light. Magnified 30 diameters. 



Lower left figure. Part of slice of diabase from dike at south end of 

 gorge one-half of a mile south of Keene. Toward upper right, a large 

 idiomorphic phenocryst of olivine with a thin magnetite or ilmenite rim and 

 much decomposed to chlorite. On left, a large idiomorphic phenocryst of 

 augite with zonal structure. Dark laths, biotite; black specks, magnetite or 

 ilmenite; white material of matrix, plagioclase. Ordhiary light. Magnified 

 23 diameters. 



Lower right figure. Part of slice of gabbro from southern side of stock, 

 2I/2 miles south-southeast of Upper Jay. Toward top, two large rounded 

 grains of olivine (with black streaks of secondary magnetite) surrounded by 

 successive rims of granulated hypersthene, plagioclase, and garnet. Dark 

 patches, hornblende. Part of large labradorite crystal at bottom, Ord'nary 

 light. Magnified 23 diameters. 



