PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 923 



Graywaeke. Griinerite and] 

 magnetite. Granite. 



No. 378H. GRAYWACKE. (Conglomerate.) 



Southeast " forty " of sec. 11, T. 59-14, Mesabi range. 

 Ref. Annual Report, xvii, pages 87, 137. 



Meg. Gray, coarsely slaty graywacke. 



Mir. Rather fine quartz and feldspar, with a finer intermixture of chlorite. 

 The feldspars are old and altered. These elements vary in grain, especially the 

 interlocking quartz, showing pebble forms, as in No. 372H. Two sections. 



Age. Keewatin. N. H. w. 



No. 379H. GRUNERITE(?) AND MAGNETITE. (Rock.) 



N. W. % sec. 14, T. 59-14, from a shaft northeast of Mesabi station. 

 Ref. Annual Report, xvii, pages 88, 137. (Compare No. 437.) 



Meg. Apparently a breccia of black slaty rock with an actinolitic cement. 



Mic. The slide contains two quite different rocks. 1. Calcite, embracing 

 crystals of grunerite(?), through which are also distributed some coarse magnetite 

 groups. 2. Taconyte in which the rounded pebbles of interlocking quartz are very 

 numerous and essentially compose the rock. The matrix of these pebbles is also a 

 coarser interlocking quartz, the pebbles being outlined by the characteristic distri- 

 bution of magnetite about their borders. There is also in this part a much coarser 

 magnetite in spreading sponge-like mesh, and in some of the angles between the 

 groups or within a circular band formed by the magnetite, is calcite, while 

 small spangles or stellar rosettes of adinolite (or griinerite) pierce the quartz in 

 places. With the exception that the taconitic structure is not visible in the 

 calcite side of the slide, the two parts are quite alike in their essential char- 

 acters, differing only in the relative proportions of the minerals. One section. 



Age. Animikie. N. H. w. 



No. 385H. GRANITE. (Decayed.) 



Three miles north of the Giant's range, on the Duluth and Iron Range railroad. 

 Ref. Annual Report, xvii, pages 89, 137. 



Meg. Coarse, hornblendic, with red orthoclase. 



Mic. There is a noticeable contrast in the apparent freshness and integrity of 

 the different minerals of this slide. There seems to have been a granitic rock or a 

 granitic debris consisting of feldspar, quartz, sphene, apatite, more or less decayed, 

 having epidote, chlorite, etc., already generated, which was microperthited and sur- 

 rounded by fresh microcline, cementing the whole into a firm rock, so that now it 

 has again the aspect of granite. One section. 



Age. Archean. N. H. w. 



