758 THE GEOLOGY OF MINNESOTA. 



[Marble. Gneiss. Quartz dioryte. Gabbro. 



altered and have given place to magnetite and to h<nrlin<jite, the latter of a yellowish 

 green color, and entirely separated from the irony ingredient, which seems to have 

 been concentrated almost entirely into the fine, crystals of magnetite which lie 

 alongside. The diallage has sometimes a faint pink or rose tint, and shows the 

 twinning 100. Biotite encloses all the other minerals, and is strongly dichroic. The 

 feldspar, having an extinction on ,. of 23, is labradorite. One section. 



Aye. Cabotian ( >') 



Ifcn/iii-/,-. This rock is petrographically, in all essentials, like the Duluth gabltro, 

 and it may be reasonably inferred that it is of the same age. It is also in the general 

 line of extension of the strike of the mass of that rock. N. H. w. 



No. 1681. MARBLE. 



West bank of the Mississippi, just below the mouth of Swan river, Morrison county. 

 Ref. Annual Report, xxi, page 154. 



Mr;/. Fine graine'd, slightly pinkish. Compare Nos. 746, 760, 1371. 

 M!<: The rock shows a fine, even grain, without impurities, and without cavi- 

 ties. One section. 



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



No. 1682. GNEISS. (Biotite quartz schM .) 



Near the centre of the S. E. % N. W. % sec. 30, T. 128-19, Morrison county. 

 Ref. Annual Report, xxi, page 154. 



Meg. Fine grained, hardly gneissic, not banded. 



Mic. The most of the rock is quartz, interlocked, but biotite is conspicuous in 

 small scales. Garnet and a little sphene are scattered sparsely in the quartz ground- 

 mass. Mixed with the interlocking quartz are numerous glassy feldspars. One 

 section. 



Age. Archeau. 



Remark. In its garnetiferous character this rock is allied to the schists at Swan 

 river and at Little Falls. It also contains similar segregations of " quartz dioryte." 



N. H. w. 

 No. 1683. QUARTZ DIORYTE(?) 



" Hardened segregations from No. 1682, similar to those seen at Little Falls." See Nos. 1670 and 1(>7'J. 

 Ref. Annual Report, xxi, page 154. 



MCI/. Fine-grained, nearly white, siliceous rock, holding crystals of hornblende. 

 N 1 1 section: 



Age. Archean. u. Si G> 



No. 1684. GABBRO. ( H<>i->ih/<-n<li<;. ) 



Philbrook, near the mouth of Fish Trap creek, northwestern corner of Morrison county. 

 Ref. Annual Report, xxi, page 155. 



