PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 293 



Oalcite and chalcopyrito. Quartzyte.] 



Meg. A very fine-grained, dark-gray, diabasic rock. 



Mic. The section is too thick for careful study. The rock is composed of small 

 plagioclase microliths, plagioclase in allotriomorphic grains, subangular, more or less 

 rounded grains of a greenish mineral regarded as augite, and magnetite. 



One section. 



Age. Cabotian(?) 



Remarks. The structure of the rock is different from that of the usual diabase 

 dykes in this vicinty. It is possible that this is a facies of the usual diabase, but it 

 is also possible that this dyke is really of later age than the rest of the dykes (Cabo- 

 tian) and represents a later intrusion (Manitou). u. s. G. 



No. 267 A. CALCITE AND CHALCOPYRITE. 



Prom No. 267. 



Ref. Annual Report, ix, page 64. 



Meg. A mass of these two minerals. 



No section. 



Aye. Cabotian(?) u. s. G. 



No. 268. QUARTZYTE. (Dark.) 



"Blackened quartzyte, with red fhernatitic) specks; from near the dike No. 267. This is of a dark color, 

 but represents the prevailing color." 



Ref. Annual Report, ix, page 64. 



Meg. A fine-grained, greenish-gray, impure quartzyte. Quartz grains and a 

 few of feldspar occur in a dark background. The hand sample contains a few red 

 spots of hematite. 



Mic. The section is composed of distinctly rounded and subangular grains of 

 quartz and some of feldspar in a dirty, greenish cement. The distinctive feature of 

 the rock is its clearly sedimentary nature, as shown by the worn quartz grains. 

 Another feature, which is shown very clearly, is the secondary enlargement of the 

 quartz grains. The feldspars are much clouded and decayed. The cement is quite 

 abundant; it is composed very largely of chlorite with some finely crystallized quartz 

 and feldspar, and much dirty undeterminable substance. 



One section. 



Age. Animikie. 



Remarks. This rock, although so near the eruptive, is very little altered. 

 Bayley has shown (Bulletin cix, U. S. Geol. Survey) that the clastic nature of the 

 quartz grains is not evident, even in the slightly altered portions of the quartzytes 

 of Pigeon point. u. s, G. 



