[HARViEj FALJ^OZOIC BRECCIA OF THE VICINITY OF MONTREAL 263 



Northwest Side of Ile Bizard.i 



This occurrence occupies an area about 150 paces in length by 50 in 

 breadth, and rises to a height of fifty-five feet, forming a bold hillock on 

 a flat country. (See plate 6.) It rests on the Calciferous formation. At 

 tlie south end, however, two large blocks of Chazy limestone are exposed 

 half way up the slope. These have been disturbed, presumably by the 

 intrusion of the breccia, so that while the nearer block has only a slight 

 dip towards the intrusive, the outer one is tilted to nearly 60°. (See 

 fig. 8.) 



Fig. 8. 



The most important inclusions of the breccia are hornstone and 

 sandstone, the latter resembling that of the Potsdam formation. In 

 lesser amount there is limestone, granite, and possibly gneiss. The 

 matrix is gray, weathering to a very strong rusty brown, and showing a 

 few large phenocrysts of pyroxene and biotite, with a more plentiful 

 scattering of relatively small flakes of biotite. Pyrite is very abundant. 

 (See fig. 7.) In general the inclusions make up a much greater bulk 

 than the paste, even amounting to as much as nincytenths of the rock. 



The cement of the breccia is made up of, — pyroxene, biotite, olivine, 

 melilite, perovskite, magnetite, pyrite and hydronephelite. ' The py- 

 roxene occurs as phenocrysts, in two varieties, augite with extinction 

 angle up to 45°, and a pale variety up to 37°. Biotite is present in less 

 amount than the pyroxene. One slide shows a cluster of basal sections, 

 also numerous scattered flakes. The olivine is generally decomposed, and 

 appears to be less in amount than the biotite. Melilite in one instance 

 is very abundant, the forms giving a dense network all through the 

 groundmass. The other slides show vague outlines in the calcite which 

 are recognized as melilite by analogy. Perovskite is everywhere extremely 

 abundant and has gi'ains of iron ore associated with it. Granular pyrite 

 is plentiful. A mineral considered to be hydronephelite is present in the 

 groundmass. In some cases it forms aggregates with definite outlines, 

 suggesting decomposition from some other mineral or fragment; again, 

 it has no regular border but is intergrown with the other minerals. 



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



Sec. IV.. 1909. 16. 



