PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 935 



Quartzytc. Diallage. Gabbro.] 



NO. 21M. QUARTZYTE. 



Sec. 18, T. 59-14, near Mesabi station. 

 Ref. Annual Report, xxii, page 88. 



Meg. Micaceous quartzyte, fine grained. 



Nic. Interlocking quartz, as in No. 8M, but more angular, with some oligodase, 

 makes up the most of this rock; the interlocking structure, however, is secondary, 

 the rock having been originally a clastic one. There is a band of darker color cross- 

 ing the slide, caused by finer quartz grains and by the presence of dark minerals 

 (iron, hornblende and sphene) accompanied by some mica which lies parallel to the 

 band. One section. 



Age. Animikie. N. H. w. 



ROCKS COLLECTED BY A. H. ELPTMAN. 



NO. 158E. DlALLAGE. 



Sec. 26, T. 61-11, Harris lake. 



Ref. Annual Report, xxii, page 185. 



Meg. Dark-green, nearly black pyroxene, conspicuously cleaved. 



Mir. One section was made approximately parallel to a cleavage (100) and 

 shows an optic axis nearly perpendicular. The extinction is not exactly parallel 

 with the other cleavages. The crystal is crowded with dark inclusions in plates 

 between the basal cleavages and more scattering ones in the clinopinacoidal cleav- 

 ages (010). It is not perceptibly pleochroic. The crystal includes, however, small 

 quantities of plagioclase, magnetite and biotite. One section. 



Age. Cabotian. 



Remark. Owing to the orientation of the section the diallagic lamellation (100) 

 is not visible. N. H. w. 



No. 178E. GABBRO (with hyperstheiic). 



N. E. % sec. 9, T. 58-10, Greenwood lake. 

 Ref. Annual Report, xxii, page 186. 



Meg. Rather coarse-grained gabbro. 



Mic. The rock presents a fine show of various minerals. The augite and oliriitc 

 were apparently slightly earlier than the feldspar, the former having taken on the 

 diallagic parting and been resorbed while still in the magma, thus presenting round- 

 ish grains of various sizes, sometimes very small. The hypersthene was latest of the 



