374 THE GEOLOGY OF MINNESOTA. 



[Graywacke. Diabase. 



Kloos terms horn-shite (Annual Report, xix, pages 109-113). The other specimen is a 

 fine-grained reddish-brown rock which much resembles the metamorphosed quartzytes 

 occuring at Wauswaugoning bay and Pigeon point. It is composed of quartz and red 

 feldspar mainly. It contains three blotches of bright red feldspar, two of which 

 blotches have centres of calcite. 



Mic. A slide from the gray specimen shows one of the usual gray wackes of the 

 region. Numerous angular and subangular, with few rounded, quartz and J'elilxjittr 

 grains are embedded in a background which is of quite fine grain. The quartzes and 

 feldspars are of all sizes up to those half a millimeter or more in diameter. The 

 fewness of rounded grains may perhaps be accounted for by secondary enlargements 

 but no grains which showed such enlargements distinctly were seen. The feldspar 

 is apparently orthoclase, anorthoclase and olit/orlase, although no grains were definitely 

 determined, and the rock seems to represent granitic debris. The feldspar is in places 

 altering to sericite and some of the grains are reddened. The background of the 

 section is a very fine-grained aggregate of quartz and feldspar with numerous chlorite 

 flakes, a few sericite (or Muscovite) flakes and some opaque gray material. The chlorite 

 flakes have their long axes usually parallel and they often bend around the larger 

 quartz and feldspar grains. Much of the quartz shows distinct undulatory extinc- 

 tion and sometimes fracturing. 



The section cut from the brown hand specimen shows a different rock. This 

 slide is composed of quartz, feldspar and chlorite. It is very similar to sections of 

 metamorphosed quartzyte from the Pigeon point region. The feldspar is abundant 

 and presents the characteristic reddened appearance so common in the Pigeon point 

 rocks; it is probably both orthoclase and anorthoclase. No quartz grains showing 

 distinct enlargements were noticed. The quartz shows undulatory extinction, but 

 the chlorite scales are not in parallel arrangement as in the other slide. This rock 

 is part of the graywacke of the region altered by a dike of basic rock, but at present 

 the rock is holocrystalline and shows no distinctly clastic structures. 



Two sections. 



Age. Animikie(?) u. s. G. 



No. 459. DIABASE (ictib quartz ami hontWt'.nde). 



Lower falls of the St. Louis river; a dike cutting the slates of the Animikie(?) in a direction north-northeast 

 at least twenty feet wide. This has so hardened the slates that they are more durable under the action of the 

 river than the dike itself. 



Ref. Annual Report, x, page 13; Bulletin ii, pages 108, 109; Final Report, vol. iv, plate A. 



Meg. A heavy, coarse, nearly black, or gray-black diabase, with hematitic spots. 



Mic. The feldspar is labnu/nrifi'. as shown by an extinction angle of 61 in a 

 section nearly perpendicular to the bisectrix ,,. It is fresh and twinned on the 

 albite, pericline and apparently on the Baveno plans. No other feldspar is present. 



