60 Canadian Record of Science. 



forms a prominent hill and the rock apparently rests on 

 the Calciferous formation. It is composed of fragments 

 of hornstone, sandstone similar in appearance to the 

 Potsdam, limestone, granite, and a dyke rock presumably 

 alnoite. The matrix is grey, weathering rusty brown, 

 and under the microscope shows a finely granular dolo- 

 mite, holding a few grains of clear quartz and plagioclase 

 feldspar. The sandstone often has a peripheral zone 

 which is decolorized and glassy, and probably represents 

 a zone of fusion. The limestone is in but small amount 

 and is wholly altered to a marble of sugary texture. 

 The fossils which it contains show it to be of Trenton age. 

 Pyrite in small cubic crystals and in veins is present in 

 the matrix and in the hornstone. 



At White Horse Rapids, on the right bank of Riviere 

 des Prairies, four and a half miles east of He Bizard (see 

 Fig. 2), there is another mass which rests on the Trenton 

 limestone. It differs, from the He Bizard exposure, in con- 

 taining anorthosite, different varieties of gneiss, and rela- 

 tively more alnoite. The matrix is coarser in grain, and is 

 light yellow in color. Quartz is in small amount but 

 forms aggregates which under the microscope with crossed 

 incols show radiate fibrous structure. 



Another locality is on the line of the Grand Trunk 

 Railway between Pointe Claire and Ste. Anne's, 2 where 

 the breccia filled a worn fissure in the Trenton limestone. 



Still another occurrence was discovered recently when 

 excavations for the foundation of the new wing of the Medi- 

 cal Building, McGill University, were in progress. Here a 

 fissure in the Trenton held a breccia principally of 

 limestone, but holding in addition a fragment of graphitic 

 gneiss of Lauren tian age. 



Probable Origin of the Breccia. From what has 

 been said above it will be seen that these isolated areas of 

 breccia are remarkably similar in character and that a 



