PETROGRAPHIO GEOLOGY AND DESCRIPTIONS. 377 



Graywacke. Clay slate. Diabase.] 



Mic. The section is very similar to that of No. 460, and has the same secondary 

 minerals, except the yellow bowlingite (?). The rock contains considerable olivine, 

 and apatite, both in short stout prisms and in long needle-like forms, is common. 



One section. 



Age. (Cabotian?) dike in Animikie(?) rocks. u. s. G. 



No. 465. GRAYWACKE. (Fine.) 



From the railroad cut, N. W. ^4 S. W. % sec. 9, T. 48-16, St. Louis valley. 

 Ref. Annual Report, x, page 15. 



Meg. Tough, gray, firm rock, hardly showing any tendency to slaty cleavage, 

 finely arenaceous. 



Mic. The section appears much like that of rock No. 456. The only variation 

 from that description necessary to apply it to this rock is to reduce the size of the 

 quartz and feldspar grains about two-thirds, or even nine-tenths; the former seems 

 to be the correct statement in examining the slide, and the latter in megascopic 

 aspect. 



One section. 



Age. Animikie(?) N. H. w. 



No. 466. CLAY SLATE. (Siliceous.) 



St. Louis river; from the falls; centre of sec. 8, T. 48-16. 



Ref. Annual Report, x, page 15; Annual Report, xviii, page 47. 



Meg. The beds here dip 334 toward the south-southwest, swinging round to 

 the south-southeast, and being then in a dip of 39 to 43. At these falls the rock is 

 less slaty, and more siliceous. Yet it breaks in the direction of the prevailing 

 cleavage easier than against it. 



Mic. The rock might be called a fine siliceous graywacke. 



One section. 



Age. Animikie(?) N. H. w. 



No. 467. DIABASE (with olivine.) 



Rock of the dike at Thomson bridge. The river at the bridge is running in the course of this dike, which 

 is about twenty-five feet wide. It is not so durable as the hardened slates on either side. Its direction is north- 

 northeast. 



Ref. Annual Report, x, page 16. 



Meg. This rock resembles the rock of the great dikes at Grand Portage and 

 Pigeon point, which there cut the slates, forming the principal hill ranges. (Nos. 

 293, 297, 298, etc.; compare, also, dike rocks Nos. 459, 460, etc.) 



Mic. It has the composition and structure of a beautifully ophitic diabase, with 

 older olivines. 



