58 Canadian Record of Science. 



conchoidal fracture. It holds, in addition to the various 

 rock fragments, small grains of glassy quartz, and feldspar 

 both fresh and kaolinized. Under the microscope the 

 following minerals were recognized, quartz, orthoclase, 

 plagioclase, and apatite, in a fine grained quartz-dolomite 

 groundmass. The quartz individuals are numerous. In 

 form they are oval, angular, or rounded hexagonal. The 

 borders are irregular, this being due, in some cases at least 

 to a deposition of secondary silica, which is in optical 

 continuity with the parent grain. The feldspar is present 

 in less amount than the quartz, and is principally ortho- 

 clase. The form is angular, but a few idiomorphic 

 individuals are present in each section. The mineral is 

 quite turbid from kaolinization, but some of the clearer 

 grains show a microperthitic intergrowth of orthoclase 

 and plagioclase. The plagioclase individuals are few in 

 number, and are twinned according; to the albite and 

 pericline laws. Apatite occurs in slender prisms, with 

 the double pyramidal terminations. 



Throughout the sections there are irregular cavities 

 filled with secondary quartz and calcite. The latter is 

 clear with well marked rhombohedral cleavage, and shows 

 faint strain shadows in polarized light with crossed nicols. 

 In the same light, the quartz is seen to have a radiate 

 fibrous structure. 



The matrix or ground mass, which makes up the greater 

 part of the section, is very fine grained, and consists of 

 quartz and dolomite with probably some calcite. A 

 qualitative analysis showed considerable insoluble residue 

 after prolonged boiling in hydrochloric acid, and the 

 solution gave heavy precipitates of iron and magnesia, 

 with a smaller quantity of lime. 



In order to more fully examine the inclusions in the 

 breccia, several types were separated from the matrix and 

 thin sections made from them. These were a granite, 

 sandstone, hornstone and limestone. 



