BY H. I. JENSKN. 123 



The hornblende occurs in idiomorphic, but highly corroded, 

 phenocrysts, which are decomposing, with the formation of 

 calcite and chlorite. In thick slices (0-04 to 06mm.) it is of a 

 brownish green colour, while in thin slices (0-025mm.) its colour 

 is light green. It is very pleuchroic in colours between brownish- 

 green and yellowish-green in thicker slices, and in the same 

 tints, though much fainter in thinner slices. Double refraction. 

 , 023. Pleochroism : ;t olive-green; b greenish; c light green. 



c> b > a. 



Species, pargasite. 



This hornblende is evidently rich in lime, as seen from the 

 decomposition products. Orthoclase is not abundant, but a few 

 clear crystals are met with, possessing a very irregular outline, 

 due to resorption. Most of it occurs, however, in the base in the 

 form of sanidine. 



Biotite of a greenish-brown colour is present in idiomorphic 

 plates, and shows the characteristic pleochroism. Magnetite 

 occurs in fair-sized crystals, but is a mere accessory. Sphene, in 

 wedge-shaped and lozenge-shaped phenocrysts, is present in the 

 same proportion as magnetite. Apatite occurs both as thick 

 stunted rods and as fine needles, and is present included in all 

 the minerals except magnetite and sphene. Chlorite, calcite and 

 kaolin are the main decomposition products present." 



The base or groundmass is of particular interest. It forms 

 about half the bulk of the rock, and contains a great abundance 

 of perfect lath-shaped microliths of plagioclase (probably albite 

 and oligoclase) and sanidine felspar, having low extinction angles, 

 and too minute for exact determination. Quartz is also present, 

 as well as a little glass. Irregular patches of this base 

 extinguish together, so that it is evident that there are 

 micrographic, cryptographic and pseudospherulitic intergrowths 

 of quartz and felspar. Such intergrowths occur also in masses 

 of definite outline shaped like felspar phenocrysts. 



