120 THE GEOLOGY OF MINNESOTA. 



[Vein matter. Zirkelyte. 



Age. Cabotian. 



Remarks. This rock seems to fall into the class named melaphyr by Pumpelly. 

 It is similar to No. 6A, in its petrographic characters. N. H. w. 



No. 1HA. VEIN MATTER IN No. 18. 



Duluth. From laminations in No. 18. 

 Ref. Annual Report, ix, page 14. 



Meg. Light greenish yellow and white, granular, but mingled apparently with 

 more or less rock matter. Apparently largely composed of a honey-like garnet and 

 calcite. 



Mic. Besides garnet and calcite the microscope reveals quartz, magnetite and 

 titaniferous magnetite, and apatite, and, further, a little gold ( ?) The magnetite is 

 in very fine particles, visible only microscopically, an alteration product. The tifait- 

 iferous magnetite is in larger grains which are frequently surrounded by a rim of gray 

 sub-opaque substance, which is taken for leiicoxene. In some cases such dark grains 

 are mostly changed to such sub-opaque substance. This mineral does not appear in 

 the midst of the calcite and garnet, but in those portions which are probably rock 

 fragments. They are microscopic rods and angular masses. They are associated 

 with quart z, epidote and secondary minute magnetite grains. A fine, white fibrous 

 mineral is probably tremolite. The small amount of gold present is associated with 

 the garnet. The only particles seen were subjected to nitric acid and remained 

 bright. The particles having been lost in the examination, the existence of gold in 

 this vein matter requires further evidence. 



Two sections. N. H. w. 



No. 19. ZIRKELYTE. ( Amyy<1<ih>i<lal.. ) 



Duluth. At the lake a short distance west of Chester creek, suddenly replaces No. 18 on the east and 

 extends about 200 feet. 



Ref. Annual Report, ix, page 14. Annual Report, x, page 36. Annual Report, xiii, pages 100, 102. 

 Bulletin viii, page xxxiii. 



Meg. A compact, almost aphanitic rock, of a dull reddish or brown color, with 

 a few scattered, brick-red feldspars a quarter of an inch long, but not enough to 

 warrant the unqualified term porphyryte for the rock. There are also some scattered 

 amygdules now filled with what appears to be epidote. These amygdules are from 

 very minute size to one-half inch across. 



Mic. Rock is composed of minute interlocking laths of.fel<lxj>ar, in a confused 

 mass of magnetite grains, yellowish granules (apparently of ejndote) and some 

 chlorite. One of the larger feldspar crystals is seen in the section; it contains small 

 flakes of a muscovite-like mineral. In general these larger feldspars are striated. 

 The brownish red color is evidently due to the fine dissemination of liematitc, which 

 colors most of the transparent grains. There is visible no ophitic structure, although 



