PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 653 



Graywacke. Green wacke.] 

 Diabase. Greenstone. 



Remark. Judging from the fact that two slides bear this number but differ 

 considerably, this rock varies from the above character to a more green, less siliceous 

 one, in which the matrix is very chloritic and calcareous and contains but few 

 quartz grains. N. H. w. 



No. 1074. GRAYWACKE. 



Near the same place as No. 1073. 



Ref. Annual Report, xv, pages 372, 396; Annual Report, xvii, pages 197, 204. 



Meg. Irregular stratum of No. 1073, holding fragments of fissile, closely jointed 

 slate. 



Mic. Only a finer grained condition of rock resembling No. 1073. One section. 



Age. Archean (Keewatin). 



Remark. The section was probably made from one of fragments of slate. 



N. H. W. 



No. 1075. GREENWACKE. 



Near the same place as No. 1073. 



Ref. Annual Report, xv, pages 372, 396. 



Meg. Collected with the purpose of showing a blending of the characters of 

 Nos. 1073 and 1074. 



Mic. The sections are so similar and so thick and the rock so fine that no 

 differences can be stated to exist between these rocks. Two sections. 



Age. Archean (Keewatin). N. H. w. 



No. 1076. DIABASE. 



Prom hills in the southern part of sec. 35, T. 65-G; south of Ogishke Muncie lake. 

 Ref. Annual Report, xv, pages 373, 374, 376, 397. 



Meg. Tough, massive, coarse jointed. 



Mir. The ophitic structure is evident, but the most of the pyroxene is altered to 

 hornblende. A section of the feldspar cut so as to show n t nearly perpendicular, and 

 in the acute angle of the optic axes, has an extinction on cleavage of 9, indicating 

 andesine, according to the determinations of Fouque. As this grain of feldspar holds 

 minute apatites it appears to be one of the original generation, but it is not, as it lies, 

 ophitic in respect to the surrounding ferro-magnesian minerals. There is also 

 considerable quartz in the rock. One section. 



Age. Archean (Keewatin). N. H. w. 



No. 1077. GREENSTONE. ("Pebbly." 1 ) 



Same place as No. 1076. 



Ref. Annual Report, xv, pages 373, 374, 397; Annual Report, xvi, page 97. 



Meg. In the field apparently graduating into No. 1070. 



