PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 575 



Dioryte. Quartzyte.] 



Mic. The section shows a quartz dioryte in which the following minerals are 

 in considerable amounts: feldspar, hornblende, quartz and iron ore. The feldspar is 

 much altered (saussuritized) and its species cannot be determined, although it is quite 

 clearly a plagiodase. As a product of the alteration much zolsite has been developed, 

 giving the feldspar a clouded appearance when examined under a low power; but 

 with a higher power the cloudiness is seen to be largely due to the presence of numerous 

 small grains of zoisite. The hornblende is brown and also green. The brown born- 

 blende may be in part original, while the green is clearly secondary, most probably 

 after augite, though no distinct augite was seen remaining. Quartz is common. The 

 iron ore, as shown by its alteration to gray leucoxene, is ilmenite; it is common. In 

 addition to these minerals there are also present chlorite, epidote, pyrite and 

 apatite. 



Two sections. 



di&inical analysi*. An analysis of dioryte, apparently from the same outcrop as No. 8C1 and closely 



similar to this number, is given by Streng and Kloos* as follows: 



SiO 2 56.59 



Al.O, 12.41 



Fe 2 0, 5.39 



FeO 10.28 



CaO 6.70 



MgO 2.02 



K 2 O 1.02 



Na 2 O 4.27 



H 2 O 1.45 



CO, - - - - trace 



Total 100.13 



P 2 6 .44 



TiO, .22 



Age. Archean. 



Remark. This rock may have been originally a gabbro with or without brown 

 hornblende and quartz. u. s. G. 



No. 862. QUARTZYTE. 



"Pinkish, white quartzyte, Garden Valley, seven miles from Merrillan, Jackson county, Wisconsin; prob- 

 ably shows Irving's 'deposited quartz.' It is also probably from this that Whitfleld's Palveacmcea irvingi was 

 obtained. (See vol. iv, page 173, Geology of Wisconsin.)" 



Kef. Annual Report, xiii, page 40. 



Meg. A white to pinkish, fine-grained, vitreous [granular] quartzyte. The 

 fracture is nearly conchoidal. 



Mic. The section shows a distinctly granular quartzyte, which is composed of 

 closely crowded, usually well rounded grains of quartz. Surrounding each grain 

 and forming a part of the cement of the rock, is a small amount of a yellowish 

 substance, which, in reflected light, is white. A thin coating of this material exists 



*EleventJi Annual Report, pp. 73, 74. 



