836 THE GEOLOGY OF MINNESOTA. 



[Diabase. Taconyte . 



The brown glass, where it surrounds the little feldspar crystals, seems to be 

 converted into a transparent glass in the immediate vicinity of the little feldspars, 

 forming a halo of light about the crystal form, visible on the removal of one nicol, 

 but invisible between crossed nicols. Also throughout the brown glass, when the 

 section is quite thin, the same phenomenon is apparent, viz., the brown glass is 

 thickly sown with spots or globules which are transparent with one nicol, and 

 invisible with both. In both cases it is probably due to incomplete crystallization, 

 from the glassy substance, the initial crystals or points of crystallization going no 

 further than the globular form and remaining mono-refringent. One section. 



Age. Manitou. N. H. w. 



No. 2068. DIABASE. (PorpJiyritic and with zirkelyte. ) 



Near the same place as No. 2066 ; a little further south. 

 Ref. Annual Report, xxiv, page 36. 



Meg. Fine-grained, dark, diabasic rock, containing numerous large porphyritic 

 plagioclases. 



Mic. This rock is qualitatively the same as No. 2077, but its crystallization is so 

 far advanced that as a whole it is worthy of a different name. 



If it ever embraced augite, it was in coarse, ophitic crystals, but no trace of augite 

 remains. There is, however, a nearly isotropic, greenish substance which occupies such 

 relation to the feldspars, and may be the result of alteration of such augite. When 

 highly magnified in strong light this green substance is resolved into a mesh of fine 

 fibres, which are in bunches or bundles, but occasionally acquire a spherulitic 

 radiated arrangement, with parallel extinction and positive elongation and low 

 double refraction, all suggesting pen nine. It is also slightly pleochroic. 



The zirkelyte of this slide is not brown, but is blackened by segregation of specks 

 of iron ore. One section. 



Age. . Manitou. N. H. w. 



No. 2069. TACONYTE. (Pebble.) 



Pebbles from the conglomerate in the hill-range south side of Puckvvunge valley, south from South 

 Fowl lake. Compare Nos. 1903 and 1904. 

 Ref. Annual Report, xxiv, page 30. 



Meg. Reddish and somewhat taconitic in fine structure. 



Mi<-. Two of the slides are of the peculiar quartzyte described as taconyte. 

 The rounded pebbles that compose the main pebble are stained with Itentaiite, and 

 they vary in the fineness of the grain of the quartz of which they are composed, 

 often seeming to be of devitrified glass or like the feldspars replaced by a fine 

 micro-granulitic growth seen in the conglomerate of Ogishke Muncie lake. In two 

 or three of the constituent granules are seen apparently remains of the green 



