506 THE GEOLOGY OP MINNESOTA. 



[Diabase. Dior.vtr. 



The hornblende is in large amount and is colorless to green, usually the latter. 

 A few brownish grains also occur. The hornblende is quite frequently fibrous, is in 

 irregular areas of various sizes and does not show crystal boundaries. It is clearly 

 a secondary or metamorphic mineral. 



The section also contains HHiytiHilc, xphcuc and numerous small prisms of 

 ii/xifift; which are most frequently short but occasionally are much elongated. These 

 apatites penetrate indiscriminately both the feldspar and the hornblende. A little 

 tfiKirtz is present. 



One section examined. 



Atjc. Cabotian. 



lii'ituirk. This rock seems to be a metamorphosed one, but what its original 

 nature was is uncertain. It might have been a gabbro or a diabase, and in this con- 

 nection we wish to suggest the possibility that this rock represents one of the diabase 

 sills, in the adjoining Animikie strata, which was somewhat altered and then meta- 

 morphosed by the gabbro contact. If this be true the diabase sills are of earlier 

 date than the gabbro, a conclusion which has some facts in its favor. (See remarks 

 under No. 709.) r. s. G. 



No. 709. DIABASE. (Altered.) 



From the top of the hill near the base of the long point on the south shore of Loon lake; probably from 

 S. W. J N. W. y sec. 35, T. 00-3 W. 



Kef. Annual Report, x, pages 83, 84, 86; Bulletin ii, page 118. 



Me<j. This rock in general is similar to No. 708. The minerals are white to 

 brownish feldspar and hornblende. 



Mlc. The section is composed of feldspar, ijrcni hornblende, chlorite, magnetite, 

 biotite, quartz, augite and apatite. The feldspar is partly kaolinized, but is usually 

 fresh and shows abundant albite twin lamellae, as well as some pericline twinning. 

 Equal extinction angles in sections normal to 010 are as high as 27, showing a 

 feldspar as basic as andesine. The hornblende is often fibrous. This mineral, the 

 chlorite, biotite, quartz and part of the magnetite, are regarded as secondary. Only 

 a small amount of augite remains. 



One small section examined. 



Age. Cabotian. 



HciiHii-k. This rock is undoubtedly from one of the diiibasc sills of the Animikie. 

 The metamorphism of such an altered diabase as this might readily, so it seems, 

 make a dioryte like No. 708. r. s. G. 



No. 710. DIOKYTK. 



This rock underlies No. 709 in the same hill, is five to ten feet in thickness and is in beds six to ten inches 

 thick. 



Ref. Annual Report, x, page 84. 



