574 THE GEOLOGY OP MINNESOTA. 



[Granite. Gneiss. Dioryte. 



shows more or less angular pieces of quartz and of feldspar in a gray, clouded matrix, 

 which appears to be, in part at least, composed of calcite. 



One section. 



Age. Potsdam. u. s. G. 



No. 858. GRANITE. 



"Average sample of the red syenyte (micaceous) at Sauk Centre, quarry of T. Carl." 

 Ref. Annual Report, xiii, pages 13, 40. 



Meg. A medium-grained, reddish-gray granite, composed of feldspar, quartz 

 and apparently biotite. Scattered through the specimen are some larger, sub-porphy- 

 ritic crystals of white feldspar, the main feldspar of the rock being reddish. 



, 'Mic. The slides show a granite, composed essentially of feldspar and a smaller 

 amount of quartz. The following other minerals are present in small amounts: 

 chlorite, biotite, magnetite, pyrite, apatite and epidote. The feldspar is much clouded 

 by alteration products and appears to be largely orthoclase with some acid plagioclase 

 and a little microcline. Two sections. 



Age. Archean. u. s. G. 



No. 859. GNEISS. 



"Average sample of the hard, dark schist, or gneiss, Sauk Centre, quarry of T. Carl." 

 Ref. Annual Report, xiii, pages 13, 40. 



Meg. A medium-grained, dark, banded gneiss, composed of hornblende, quartz 

 and feldspar. 



Mic. The section shows a granitic aggregate of quartz and much clouded 

 feldspar with more or less green hornblende, chlorite, magnetite, biotite, epidote and 

 sphene. One poor section. 



Age. Archean. u. s. G. 



No. 860. GNEISS. 



" Sample of the schist showing considerable mica, Sauk Centre." 

 Ref. Annual Report, xiii, pages 13, 40. 



Meg. A banded gneiss composed of hornblende, quartz and feldspar, with much 

 rusty biotite along the cleavage planes. 



Mic. The section is composed essentially of quartz (in great abundance), much 

 clouded feldspar, green to blue-green hornblende and chlorite. One section. 



Age. Archean. u. s. G. 



No. 861. DIORYTE. 



"Average sample of the massive dioryte, Sauk Centre." 



Ref. Annual Report, xiii, pages 13, 40. The same rock is described in Annual Report, xi, pages 72-74, 104. 



Meg. A dark-gray, medium-grained, granitic rock composed essentially of 

 hornblende and feldspar. 



