P^ETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 599 



Breccia. Quartz-porphyry.] 



No. 912. BRECCIA. (Pyritic.) 



Lee mine, Tower. 



Ref. Annual Report, xv, pages 248, 389. 



Meg. A breccia in which the fragments are rather soft, earthy hematite, and 

 the cement is pyrite and hematite. There is present a small amount of a soft, green, 

 chloritic or earthy substance as a part of the cement. 



No section. 



Age, Keewatin. u. s. G. 



No. 913. QUARTZ-PORPHYRY. ( Hornblendic. ) 



Low hills, southeast of Tower, near the Duluth and Iron Range railroad; sec. 33, T. 62-15 W. 

 Ref. Annual Report, xv, pages 271, 273, 389. 



Meg. The rock is gray in color and is apparently somewhat schistose. It shows 

 a very fine-grained groundmass in which are small porphyritic crystals of hornblende 

 and larger ones of feldspar and quartz. 



Mic. The rock is a quartz-porphyry, which has been altered and sheared, and 

 the section is too thick for careful study. The porphyritic crystals are feldspar, 

 quartz and hornblende. The feldspar is considerably kaolinized and clouded; some 

 of it shows no twinning and is perhaps orthoclase, while some of it is twinned 

 according to the albite law and is perhaps near oligoclase. The quartz is not abundant; 

 two of the crystals show an approach, though somewhat rounded, to a bipyramidal 

 form. The hornblende varies in color from brownish, to green, to almost colorless; 

 it is frequently fibrous and perhaps none of it is original, although some of the 

 brown crystals may be. 



The groundmass of the rock is very fine grained and is composed of quartz, 

 feldspar, flakes of hornblende, of chlorite and of muscovite, and epidote. The last 

 named mineral is sometimes in distinguishable grains, and also, apparently, as very 

 minute grains scattered all through the groundmass. 



One section. 



Age. Keewatin. u. s. o. 



NO. 914. QUARTZ-PORPHYRY(?) 



Southeast of Tower, near the Duluth and Iron Range railroad; sec. 33, T. 62-15 W. 

 Ref. Annual Report, xv, pages 271, 273, 389. 



Meg. A fine-grained, gray rock, containing some large porphyritic quartzes 

 and some smaller, less apparent feldspars. 



Mic. The most noticeable feature of the section is presence of an abun- 

 dance of epidote, which has permeated the whole rock; it is scattered in small 

 grains throughout the groundmass, which is mainly composed of fine-grained 

 quartz, and it replaces what appear to have once been porphyritic feldspars. There are 



