PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 757 



Dioryte. Slate. Greenstone. Gabbro.] 



No. 1671. DIORYTE (?) ( with quartz) . 



Same place as No. 1670. 



Ref. Annual Report, xxi, page 154. Compare Annual Report, xxiv, pages 3-10. 



Meg. Fragment of the hornblendic layer which encloses the segregation shown 

 in No. 1670. 



Hie. Like No. 1670 except that the garnets are nearly absent, being very small 

 and scarce. One section. 



Age. Archean (Keewatin). 



Remark. Rocks Nos. 1670 and 1671, having been called " quartz dioryte " by 

 Streng and Kloos, we prefer not to change from their designation, although there are 

 some peculiarities of structure which might warrant another name. This rock is not 

 an eruptive, but forms isolated knots in the garnetiferous schists of the place, these 

 knots varying in size from a few inches to a foot or two. They are indigenous in the 

 slates in the same manner as granitic knots are sometimes seep in schists. N. H. w. 



No. 1672. DIORYTE (with quartz). 



Same place as No. 1670. 



Ref. Annual Report, xxi, page 154. 



Meg. Similar to No. 1670. A dense, fine-grained black rock with porphyritic 

 hornblendes and garnets. No section. 



Age. Archean (Keewatin). u. s. G. 



No. 1673. SLATE. (Garnetiferous. ) 



Little Falls, on the Mississippi river, in Morrison county. 

 Ref. Annual Report, xxi, page 154. 



.]////. A rather fine-grained, black, slaty rock, containing porphyritic garnets 

 and also apparently some hornblendes. No section. 



Age. Archean (Keewatin). u. s. o. 



No. 1677. "GREENSTONE." 



Randall, Morrison county. 



Ref. Annual Report, xxi, page 154. 



Meg. A roughly schistose, siliceous and also calcareous, rusty-weathering, 

 indefinite greenstone. No section. 



Age. Archean (Keewatin). u. s. G. 



No. 1678. GABBRO (with Uotite}. 



Quarried at Little Falls, Morrison county, on the west side of the river. 

 Ref. Annual Report, xxi, page 154. 



Meg. Having much the aspect of the gabbro at Duluth. 



Mif. The rock is slightly ophitic, but some of the augite was earlier than the 

 feldspar, and takes the form of t/i((//ii</<>. It encloses the olivines, which are wholly 



