570 



THE GEOLOGY OP MINNESOTA. 



[Taconyte. 



Mic. In ordinary light the slide presents a reddish appearance, due to finely 

 disseminated hematite dust. Frequently small roundish granules are seen more or 

 less distinctly outlined. These granules are the common feature of taconytes. 

 Under crossed nicols the rock is seen to be composed mainly of very fine-grained 

 tjttarfz, both in and around the granules. So the granules are not so distinct under 

 crossed nicols, although some of them can be seen, owing to an occasional variation 

 in fineness of grain. A little magnetite is present. 



One section. 



Age. Pebble in Potsdam conglomerate. u. s. G. 



No. 852B. TACONYTE. 



Pebble in No. 852. 



Ref. Annual Report, xiii, page 40; American Geologist, vol. xvi, page 157, figure 2. 



Meg. A red taconyte pebble, composed of red granules, usually smaller than 

 a pin's head, in a matrix which is very fine grained, almost glassy. 



Mic. The slide shows granules, composed of hematite and fine-grained quartz, 

 in a matrix of fine-grained quartz. The accompanying figure, magnified about 

 thirty diameters, shows the nature of this rock. In the figure the black represents 

 hematite, and the white, both in and between the granules, represents very fine- 

 grained quartz. 



One section. 



Age. Pebble in Potsdam conglomerate. u. s. G. 



FIG. 32. TACONYTE IN NO. 852B. FIG. 33. TACONYTE IN NO. 852C. 



No. 8520. TACONYTE. 



Pebble in No. 852. 



Ref. Annual Report, xiii, page 40; American Geologist, vol. xvi, page 157, figure 3. 



Meg. A reddish rock, appearing like a fine-grained, impure quartzyte. Consid- 

 erable hematite is present. 



