PETROGRAPHIO GEOLOGY AND DESCRIPTIONS. 875 



Diabase. Graywacke.] 



No. 2257. DIABASE. ( Umlitized. ) 



Same place as No. 2256. 



Ref. Annual Report, xxiv, page 79. 



Meg. Same rock, but having small masses more hornblendic and green in which 

 are small aggregations of hornblende arranged radiatingly and ophitically. No section. 

 Aye. Igneous greenstone cutting the Upper Keewatin. N. H. w. 



No. 2258. DIABASE. (Uralitized.) 



Thirty paces north of the quarter-post, west side of sec. 33, T. 64-0. 

 Ref. Annual Report, xxiv, page 79. 



Meg. Coarser condition of the rock last mentioned, forming a rough country, 

 the ridges running a little north of east. The coarse hornblendes stand above the 

 weathered surface. 



Mic. The secondary hornblendes embrace the altered feldspars in the ophitic 

 manner, and are sometimes interpenetrated and embraced in the same manner by 

 leucoxene. The products of alteration of the feldspars are epidote, an isotropic, chlo- 

 ritic substance, and apophyllite. The epidote is abundant in granular aggregates so 

 fine and so highly refractive that they show no polarization colors, but, between the 

 nicols, present a nearly isotropic field. It also rises into grains of considerable size. 

 The mineral here identified as apophyllite is scattered quite commonly throughout 

 the slide, having low single and double refraction, appearing much like a secondary 



feldspar. It is sometimes in large plages which 

 embrace much epidote. It has a parallel extinction, 

 some of the crystals being much elongated and 

 usually negative, having n f parallel with their length, 

 but not invariably. In numerous instances these 

 elongated crystals are nearly isotropic except along 

 a narrow margin, and sometimes different orienta- 

 tions appear in the same mass. The accompanying 



FIG. 50. BASAL SECTION OF APOPHYLLITE . , 



IN NO. 2238. diagram represents an oblique basal section. Ine 



central area is biaxial and has n f as acute bisectrix, extinguishing at about 45 from the 

 point at which the peripheral portion extinguishes. This mineral was later in origin 

 than the hornblende and epidote, enclosing both, epidote also being enclosed by the 

 hornblende. It serves, apparently, as a background in much of the rock. ' One section. 

 Age. Igneous greenstone cutting Upper Keewatin. N. H. w. 



No. 2259. GUAYWACKE. 



Prom a conglomeratic ridge running northeastwardly, lying some distance north of the west quarter-post 

 of sec. .33, T. 64-9. 



Ref. Annual Report, xxiv, page 79. 



