[harvie] paleozoic BRECCIA OF THE VICINITY OF MONTREAL 269 



the breccia just northwest of the quarry contains a literal network of 

 dykes and illustrates the shattered nature of the rock in the vicinity of 

 the breccia. The whole arrangement of the patches of breccia and as- 

 sociated dykes strongly suggest a zone of shattering crossing the end of 

 the mountain. 



The inclusions found in these occurrences are, — limestone, sand- 

 stone, muscovite and hornblende granites, syenite, syenite porphyry, 

 gneiss, essexite and a pyroxene-hornblende rock. The limestone is, of 

 course, the most abundant inclusion, being derived from the Trenton of 

 the wall rock. The sandstone has apparently come from the Potsdam. 

 The syenite is composed of orthoclase and biotite. The syenite porjshyry 

 consists of groups of felspar phenocrysts, chiefly orthoclase and albite, in 

 a fine-grained groundmass of alkalai felspars with a little biotite. The 

 inclusion called essexite is probably the same as the pyroxene-hornblende 

 rock of which a section was examined. It is composed essentially of 

 hornblende with smaller amounts of augite and nepheline. 



The cement of these various masses and dykes of breccia was found 

 to have been derived from one. common magma. For this reason it has 

 been thought well to separate the petrography from the general descrip- 

 tive matter and to treat it in one separate paragraph. 



The largest mass of the breccia and the one containing the most 

 abundant and freshest igneous material, namely that at the Westmount 

 quarry, is believed to show the true character of the paste. Five sections 

 were examined. The rock is of a very dark green colour and rapidly 

 becomes rusty on weathering. The texture is medium grained, slightly 

 porphyritic, with a tendency for the dark minerals to form clusters I'ound 

 the phenocrysts. The photomicrographs (figs. 18 and 13) show a typical 

 field in a thin section of the rock. 



In composition the rock is essentially augite, felspar and nepheline, , 

 with lesser amounts of hornblende, biotite, nosean, sphene, apatite, ilme- 

 nite and pyrite. The augite occurs as phenocrysts, both large and small, 

 having a pinkish brown color with slight pleochroism : zonal structure is 

 pronounced and the dispersion of the axes very high. The larger indi- 

 viduals show resorption fringes of green hornblende, while many of the 

 smaller ones have been completely changed by this action. In one slide 

 primary hornblende is found as a few good basal sections. The felspar 

 is chiefly orthoclase, found as lath-like individuals having Carlsbad twin- 

 •img and occasionally showing a somewhat spherulitic arrangement. 

 Some plagioclase is also present. Nepheline is rarely found unaltered, 

 being generally represented by hydronephelite and occasionally a little 

 cancrinite. The hydronephelite was confirmed by a gravity separation. 

 Biotite occurs as a few large well-formed individuals, but is most com- 



