Geology cf St. Helen's Island. 59 



The granite was a light colored, medium grained 

 rock, consisting wholly of quartz and feldspar. Under 

 the microscope it presented the usual hypidio-morphic 

 structure. The feldspar was principally ortho-clase, 

 with subordinate amounts of plagioclase and microcline. 

 The individuals were large with irregular borders, 

 which interlocked with one another and with the 

 quartz. Many of the grains were almost opaque owing 

 to a heavy deposit of limonite along the cleavage planes. 

 The quartz is traversed by cracks and holds minute hair- 

 like inclusions. A few small grains of magnetite and 

 hematite were also noted. 



The sandstone selected was fine grained, and light 

 brown in color. Microscopically it consisted of quartz, 

 with a small amount of feldspar, the grains being 

 cemented by silica and limonite. The quartz grains were 

 rounded, or irregular through secondary growth. Of the 

 feldspar the orthoclase was turbid, while the plagioclase 

 was clear and finely twinned polysynthetically. 



The hornstone was a dark, almost black rock, of dull 

 lustre, and brittle with conchoidal fracture. Under the 

 microscope it was seen to consist of minute grains of 

 calcite, quartz, and pyrite. There were many spots of 

 dark carbonaceous matter scattered throughout the sec- 

 tion. 



The limestone examined was a typical Trenton speci- 

 men, being made up of fragments of brachiopods, crinoids, 

 and corals, held together by a calcite cement. 



Other Occurrences of Breccia. Before inquiring 

 into the origin of this breccia, a brief description of the 

 other exposures will be given, in order to show their 

 similarity with the typical occurrence. The He Konde 

 development is an extension of that of St. Helen's Island 

 and smiilar to it in all respects. 



On the north end of He Bizard 1 (fig. 2), the breccia 



1. Geology of Canada, 1863, p. 357. 



