PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 495 



Forellenstein. Gabbro. Cumberlandyte.] 



minerals, such as are frequently seen much altered. It cannot be due to greater 

 surface abrasion by the glacial epoch, exposing the fresher masses, since where such 

 abrasion certainly occurred, these rocks [/. e., the Keweenawan] are often seen to be 

 still greatly altered. It is left to infer that by far the greatest amount of such 

 alteration is not due to weathering, but to some cause in the original environment 

 of the rocks themselves. N. H. w. 



No. 693. FORELLENSTEIN. 



West end of Poplar lake, at the portage to Duck lake; N. W. % S. E. % sec. 2, T. 64-2 W. 

 Ref. Annual Report, x, pages 79, 80, 84; Bulletin ii, page 91. 



Meg. A gray rock, rusty in appearance; is of granitoid texture and rather coarse 

 grained; composed of plagioclase, magnetite and olivine. 



Mic. The section is composed essentially of plagioclase, in small part kaolinized, 

 in <iij net He in abundance, and nlirinc. The plagioclase, as well as the olivine, is con- 

 siderably fissured and the fissures are frequently filled with a yellowish stain. On 

 the peripheries of some of the magnetite grains are small biotitc scales; and a very 

 small amount of augite is present. 



One section examined. 



Age. Cabotian. u. s. G. 



No. 694. GABBRO Civitli olivine ). 



South shore of Iron lake, a little east of the west line of sec. 33, T. 65-2 W. 

 Ref. Annual Report, x, pages 80, 84; Bulletin ii, page 89. 



Meg. A dark-gray granitoid rock, composed of gray feldspar 3nd a large amount 

 of black material which seems to be mostly magnetite. 



Mic. M. E. Wadsworth's description of this rock is as follows:* 



" The section is composed of plagioclase, some possible orthodase,diallage, olivine 

 and marjnetite. The latter is partially surrounded by well marked biotitc borders, 

 while it contains inclusions of the same. One of the olivines, which is apparently a 

 unit in common light, its form and fracture lines indicating this, is seen in polarized 

 light to be made up of four individuals. A little biotite occurs, but it is not attached 

 to the magnetite. " 



One section. 



Age. Cabotian. u. s. G. 



No. 695. CUMBERLANDYTE. 



North shore of Mayhew lake; E. L S. E. y sec. 36, T. 65-3 W. 

 Ref. Annual Report, x, pages 48, 80, 81; Bulletin ii, page 



Meg. The rock is a rather coarse-grained aggregate made up very largely of 

 titaniferous magnetite. Numerous olivine grains can be seen, and also a few 

 feldspars. 



*Bullelin ii, p. 89. 



tThe section described on page 109 of Hulletin ii was not made from the hand specimen of this numlx>r. 



