564 THE GEOLOGY OP MINNESOTA. 



[Shale. Quartzyte. Granite. 



No. 833. SHALE. (Red and sandy.) 



The lowest rock seen in the railroad cut at Redstone, near New Ulm. 

 Ref. Annual Report, x, page 121. 



Meg. A fine-grained, red, sandy shale; an impure sandstone. 

 Mic. The section shows a rock in general similar to No. 832, but with less 

 quartz and a much larger amount of red iron oxide. 



One section. 



Age. Potsdam. u. s. G. 



No. 834. QUARTZYTE. (Red.) 



"Slab of red quartzyte from Sioux Palls, showing the finely pitted exterior of the individual sand grains 

 on the removal of the white schist, No. 830." 

 Ref. Annual Report, x, page 121. 



Meg. No hand specimen found. 

 No section. 



Aye. Potsdam. u. s. G. 



No. 835. GRANITE. ( Coarse-grained. ) 



Prom the quarries at East St. Cloud. 



Ref. Annual Report, x, pages 107, 121, 122; Final Report, vol. i, pages 196-199. 



Meg. A coarse-grained, gray to yellowish-gray granite, composed of feldspar, 

 quartz, hornblende and biotite. 



Mic. The section shows feldspar, quartz, dark, brownish-green, almost opaque 

 hornblende and biotite. The feldspar and quartz, especially the former, are in large 

 and also in small grains, the two interlocking closely, and the large grains do not 

 show their crystal form. The feldspar, while not carefully studied, still appears to 

 be of four varieties: (1) Clouded, untwinned orthodase; (2) Pai/u'tr in large grains; 

 (3) Very finely twinned anorthoclase; (4) Plagioclase near oligoclasc. One section. 



Chemical analysis. An analysis of this rock gave the following results: 



SiO 2 - 74.70 



A1 2 O 3 12.30 



Fe 2 3 and FeO 3.19 



CaO 1.51 



MgO . .2.-, 



K 2 2.25 



Na 2 - 1.91 



Total 96.13 



Age. Archean. u. s. o. 



No. 836. QUARTZYTE. (Pinl-.J 



"No, 836, the pink quartzyte known as the 'jasper rock' locally, from Sioux Palls, Dakota. This is a 

 pinkish granular quartzyte, but with a cement that, on disintegration, allows the rock to become a white sand." 

 Ref. Annual Report, x, page 1'22. 



Meg. A fine-grained, compact, pinkish quartzyte. Along cracks a soft, earthy, 

 white material occurs in small quantity. 



