376 THE GEOLOGY OP MINNESOTA. 



[Diabase. 



No. 461. DIABASE. 



Same locality as No. 460. From a dike eight feet wide. 

 Ref. Annual Report, x, page 13. 



Meg. A fine-grained, dark-gray, diabasic rock with a few small porphyritic 

 crystals of plagioclase. 



Mic. The section, which is rather thick, shows small plagioclases, mostly lath- 

 shaped, in a confused, dirty, greenish groundmass of alteration products. The 

 plagiociase and part of the magnetite are the only original minerals present. What 

 the original nature of the groundmass was is uncertain, but it seems probable that 

 it was largely augite and the rock a diabase. 



One section. 



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



No. 462. DIABASE. 



From a dike crossing the river at the mouth of the creek coming from the north on S. W. % sec. 10, T. 

 48-16. It is about 30 feet wide, and is less durable than the hardened slate. 

 Ref. Annual Report, x, pages 14, 19. 



Meg. Dense, black and fine grained, but sparsely porphyritic, with feldspars of 

 the earlier consolidation. 



Mic. The thick section only shows that the rock is composed essentially of 

 plagioclase, augite, magnetite, and that the augite was earlier than the feldspar. 



One section. 



Age. (Cabotian?) dike in the Animikie(?) N. H. w. 



No. 463. DIABASE. 



From a dike eight feet wide running north about 15 E. on the N. E. % S. E. ^ sec. 9, T. 48-16, crossing 

 the river. 



Ref. Annual Report, x, page 14. 



Meg. The rock is medium grained, dark (nearly black), and has small, metal- 

 loidal reflections, appearing like pyrite. 



Mic. The much decayed section shows the augites were principally earlier than 

 the feldspars, and that long magnetite rods have been generated. 



One section. 



Age. (Cabotian?) dike in the Animikie(?) N. H. w. 



No. 464. DIABASE (with olivine). 



"From a dike crossing the river a short distance above the last [No. 463], in the same direction, but thirty 

 feet wide." 



Ref. Annual Report, x, page 14. 



Meg. A rather fine-grained, dark -gray diabase. 



