PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 523 



Conglomerate.] 



Mic. The section is composed essentially of a carbonate which is much clouded 

 and semi-opaque. In places it shows absorption. On treatment with hydro fiuosilicic 

 acid numerous crystals of the silicic fluoride of calcium appeared, together with quite 

 a number which are characteristic of either magnesium or iron compounds. The 

 rock is composed largely of calcite, with considerable FeC0 3 and also, very probably, 

 some MgC0 3 . In the section is an irregular vein of irregularly interlocking grains 

 of quartz, which is somewhat clouded. On the sides of the vein the quartz is much 

 liner grained, and it commonly shows undulatory extinction. The vein thus appears 

 to have been crushed. 



One section examined. 



Age. Keewatin. u. s. G. 



No. 744. CONGLOMERATE. ( Matrix.) 



Campers' island in Ogishke Muncie lake. This island is just west of the narrows of the lake in sec. 23, 

 T. C5-0 W., and is near the centre of S. } S. 1 3 of this section. 



fief. Annual Report, x, pages 91, 92, 95; Annual Report, xvii, pages 194, 205; Bulletin ii, pages 128, 129. 



Met/. There are two varieties of specimens with this number. The tirst was 

 collected in 1879 and there may have been some mistake in numbering the speci- 

 mens, for they do not represent the main characters of the matrix of the conglom- 

 erate on Campers island. M. E. Wadsworth examined these specimens and slides, 

 calling the rock porodyte; his description is as follows:* 



"A fine-grained, greenish rock of a compact structure and conchoidal fracture. 

 Contains some pyrites. The sections are grayish green and composed of altered 

 andesitic fragments. This andesyte was originally made up of tabular plagioclastic 

 feldspars in a fine felty groundmass. The feldspars and groundmass have now been 

 altered to an aggregation of chlorite and colorless mica scales, secondary feldspar, 

 wtit/netite and pi/rite. The feldspars retain their forms and sometimes traces of twin- 

 ning. The colorless mica is, in this section, in larger scales than those before seen, 

 and it possesses the cleavage and optical characters of muscovite, to which mineral it is 

 here referred." 



The other specimens were collected several years later and they represent the 

 main mass of the matrix of the conglomerate of the island. These were taken from 

 the north side of the blunt point at the southwestern corner of the island, where 

 there are extensive exposures. These specimens show a rather coarse-grained, gritty, 

 gray rock which is plainly fragments.!. Some of the component grains are well 

 rounded, and this is usually the case with larger pebbles contained in the matrix. 

 The most noticeable grains of the rock are quartz and feldspars, and small flinty frag- 

 ments are common. 



^Bulletin ii, pp. 1-28, 129. 



