710 THE GEOLOGY OF MINNESOTA. 



|Grp*>nwacke. Diorj-te. 



Met/, firitty greenstone. 



Mir. In the slide are the outlines of numerous large pieces of feldspar crystals, now 



wholly tilled with the usual elements of this rock, viz.: rli/orift; ailritf, etc.. only differ- 



ing from the rest of the rock in being more brightly transparent in common light, and 



more dark between crossed nicols. The rock is well charged with nitrite. One section. 



Aye. Archean (Keewatin). N. H. \v. 



NO. U'.NI. (ilv'KK.XWACKK. 



The same from the ea.-t side of the east hay of Saddle Hags lake. 

 Kff. Annual Report, xvi, pages ',18, 123. 



( i reenstone. 



Mic. This rock varies, not so much for having had original fragments of 

 feldspars, as from being more abundantly supplied with the substance that has given 

 it isotropic areas. Some of these appear like old vesicular scoria. Otherwise it is 

 like th6 last. One section. 



.\yc. Archean I Keewatin ). N. H. w. 



No. 13H1. DlOKYTKf?) (<;r,'i'i,.vt<,>i<:) 



West side of Frog Rock lake. 



AV/. Annual Report, xvi. pages !)S, lit. 



Met/. (ireen ;iii(l rather massive. 



Mn-. Conspicuous forms of itnt/itr and of feldspar are the first noticeable 

 feature. This uralite came from a twinned pyroxene, which is still preserved in the 

 twinning atid in the idiomorphic outlines of some of the sections. These lie in a 

 matrix which appears fragmental, made up of similar materials in finer grains with 

 considerable rltlorife. The rock is less altered than most of the foregoing green- 

 wackes, but more altered than the similar tuffaceous rocks (as No. 1049, etc.) seen 

 about Kekequabic lake and about the lakes westward from there. The rock shows 

 much feiicH.mir and fhlorHir isotropic material, some m/rite and apparently a little 

 c/iitlotc. One section. 



Age. Archean (Keewatin). 



Renxn-k. It remains uncertain whether this rock is an altered diabase, or a 

 debris of basic rock. N. H. w. 



No. 13H2. DiOKYTE(?) 



Near the centre of sec. 19, T. 65-5, south of Frog Rock lake. 

 Ref. Annual Report, xvi, pages 98, 123. 



Same kind of rock as the last. 



Mic. Much of the rock is isotropic, occupied by the well-known chloritic 

 substance, but there are outlines of crystals and parts of crystals of feldspar, all much 

 decayed. Of calcite and of nralite there is less than in No. 1381. One section. 



Age. Archean (Keewatin). N. H. w. 



