368 THE GEOLOGY OF MINNESOTA. 



[Jaspilyte. Sandrock. 



from their fellows. The result seems to be a partial preservation of the original 

 cellular arrangement, as well as a more perfect crystallization of the iron into 

 magnetite. The calcareous surroundings have been entirely replaced by silica, the 

 exact outlines of each cell are more or less revealed by the positions of the opaque 

 magnetite-dust clusters, and by the transparent lines that surround and separate 

 them. When the greensand was broken and disseminated loosely, it seems to have 

 been gathered, under the same dynamic force, into larger magnetite crystals and 

 spicules, some of which appear in the same slide from which the foregoing drawings 

 are taken. A photograph of this slide is represented by figure 8 of plate I.* 



Two sections. 



Age. Animikie. N. H. w. 



No. 442. JASPILYTE. 



From the shallow pit dug for silver by the Chester expedition of 1875. About half a mile south from the 

 from the last; S. E. % sec. 11, T. 59-14 



Bef. Annual Report, ix, page 109; Annual Report, xi, page 159. This is the same rock as No. 1642, Bulle- 

 tin vi, page 203. 



Meg. A fine-grained, somewhat gray or greenish quartzyte which in the field 

 is somewhat banded with iron ore, and is associated with greenish graywackes and 

 schist similar to the schists at Tower. 



Mic. The section shows a characteristically fine siliceous rock which consists 

 wholly of quartz. 



One section. 



Age. Archean (Keewatin). 



Remark. This locality is discussed and illustrated by a diagram in Bulletin vi, 

 pages 203, 204. The nature of this jaspilyte is greatly in contrast with that of No. 

 441. The two are found here in close proximity, yet they maintain their own 

 characters. This rock is also illustrated by No. 1642. N. H. w. 



No. 443. SANDROCK. 



Near Fond du Lac, near the centre of sec. 2, T. 48-15 W. 



Ref. Annual Report, x, pages 9, 30; Final Report, vol. i, pages 200-203. 



Meg. Light-colored, coarse, approaching a conglomerate, with lenticular thin, 

 interpositions of green shale which are sometimes an inch in greatest extension. 



Mic. Along with many angular quartzes and microcline fragments is a large 

 ingredient of aporhyolyte, or devitrified glass, the glass being more evident in the 

 gray portion and the aporhyolyte in the red. Hematite is the coloring element, but 

 is more abundant in connection with the aporhyolyte. Occasional grains of biotite, 

 chlorite and amorphous leucoxene ( ?) are also present. 



* Compare W. D. MATTHEW. On phosphate nodules from the Cambrian of Southern New Brunswick Transactions of 

 the New York Academy of Science, vol. xii. April 10, 1893. 



