PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 885 



Gabbro. Diabase. Zirkelyte.] 



Mic. The augite, olivine and feldspar were formed about simultaneously, but 

 occasionally the augite surrounds the oliviue. There is considerable magnetite, 

 which was later than the feldspars and olivine. While most of the augite is granular, 

 some is ophitic, as if there had been two dates at which it was generated. There is 

 also some quartz which enters the feldspar in a granophyric manner (Plate V, figure 

 6). One section. 



Age. Cabotian. 



Ranin'k. This is one of the largest known sills and can be traced, with inter- 

 ruptions, as far as to Arrow river, where it seems to have its strike into Canada, 

 although it appears (as supposed) in similar hills further east along the boundary. 

 Its thickness is about 100 feet at mount Reunion. N. H. w. 



No. 2065. GABBRO. 



Eastern part of Rove lake. Prom a sill near the water on the south side ; one and one-half miles eaat of 

 mount Reunion. 



Ref. Annual Report, xxiv, page 31. 



Meg. Fine grained. 



Mic. So far as concerns structure and composition, this rock is like that of the 

 great sill of mount Reunion, except in being finer grained, and in having decayed so 

 much that no olivine is preserved and the augite is mostly uralitized. 



Age. Cabotian. N. H. w. 



No. 2066. DIABASE. ( Amygdalmdal. ) 



Summit of hills just south of the conglomerate (Nos. 1902, 1903 and 1904). Probably in N. E. % sec. 25, 

 T. 64-3 E. 



Ref. Annual Report, xxiv, page 35. 



Meg. A fine-grained, dark-gray, diabasic rock, with chalcedonic amygdules. 

 No section. 



Age. Manitou. u. s. G. 



No. 2067. ZIRKELYTE. ( Basalt glass. ) 



Near the same place as No. 2066. 

 Ref. Annual Report, xxiv, page 36. 



A fine-grained, light-gray, rather soft rock, looking like a decayed basic 

 eruptive. Compare No. 1905 which somewhat resembles this rock. 



M/r. The slide shows a rock that consisted very largely of basic glass, but now 

 contains, along the numerous fissures by which it is parted into somewhat perlitic 

 areas, much calcite, and frequent minute feldspar crystals which have lost their 

 power of individual polarization by the substitution of kaolinic products of alteration. 

 These fissure-lines are more transparent than the glass itself, which is brown, and 

 in them are nearly all the crystal forms visible. Sometimes these fissure-lines 

 take shapes and directions that suggest a fluidal origin at the commencement of 

 flowage. 



