264 ROYAL SOCIETY OF CANADA 



A small exposure on the fiat at the north end of the hill shows the 

 igneous material forming the greater proportion of the rock. Specimens 

 from here are quite free from the rusty weathering so noticeable a feature 

 in the first case. The paste is greenish gray in colour, showing very 

 numerous phenocrysts of pyroxene, some enormous olivines up to two 

 inches across, also a few biotites, and a number of amygdules filled with 

 a zeolite. 



Thin sections show the rock to be composed of, — pyroxene, biotite, 

 garnet, perovskite, chlorite, serpentine, hydronephelite and a zeolite. 

 The pyroxene is present as remnants of phenocrysts, the maximum ex- 

 tinction angle obtained being 24°. In the slides examined the olivine 

 was wholly altered to serpentine. Biotite is small in amount, some of it 

 being much bleached. Secondary mica is quite abundant. Granular ag- 

 gregates of garnet form a large proportion of the slide. Some remark- 

 able globules of chlorite are probably secondary after garnet crystals. 

 Perovskite is very plentiful in rather large octahedra. Hydronephelite 

 forms the groundmass, being well seen in one portion where it was found 

 quite fresh. Zeolites giving straight extinction, probably natrolite are 

 found in the amygdules. 



About three-quarters of a mile southwest of this last occurrence, 

 there is another small outcrop of a similar breccia, but it is so much 

 covered with drift that the relations could not be ascertained. 



White Horse Eapids. 



On the banks of the Eivière des Prairies at the White Horse Eapids, 

 about four and a half miles east of the northern occurrence of breccia on 

 Tie Bizard, there is another of the same description, occupying a some- 

 what larger area, and resting on the Trenton limestone.^ There are a 

 number of specimens from this locality in the Petrographical Museimi 

 of McGill University, but no notes as to their relations. This, of course, 

 limits the present work to a mere description of these specimens. 



The specimens show limestone, shattered limestone, breccia and a 

 dyke rock. The breccia is made up of fragments of sandstone and lime- 

 stone, (both partly altered, to quartzite and to marble), hornstone, anor- 

 thosite, white biotite-granite, pink granite, syenite, and grains of felspar. 

 The fragments, chiefly limestone, are much rounded, giving a spheroidal 

 appearance on fractures, whilst the paste, having largely decomposed to 

 yellow chlorite, gives the rock a light colour. 



Thin sections did not yield much more information than the hand 

 specimens. The cement of the breccia is chiefly a carbonate with lesser 



1 Geology of Canada, 1S63, p. 357. 



