5o6 ERNEST HOWE 



Like the others, they are very completely mashed and contain both 

 feldspar and biotite, but the amount of quartz is largely in excess of 

 that of all the other minerals. The occurrence of massive quartzite 

 v\^ith the Irving greenstones has already been referred to, and it seems 

 more than likely that these siliceous schists are quartzites that lay 

 within zones of great mashing and suffered with the rest of the rocks. 



Structure. — It has not been possible to find any evidence of original 

 bedding in the Irving greenstones, although frequently, on account 

 of their schistosity, the rocks appear to be stratified. This banding, 

 though predominant, is not a constant feature, and transitions may 

 be observed from schists to unmashed rocks which have the compo- 

 sition and textural characteristics of intrusives. In addition to the 

 schistosity, which is generally vertical and with a northwest-southeast 

 strike, the massive greenstones, more especially near their contact 

 with the Algonkian conglomerates and quartzites, have been frac- 

 tured and brecciated. These conditions were probably brought 

 about at the time that the shearing and complicated infolding took 

 place between the Algonkian sediments and the Irving greenstones. 

 In a very few cases it has been possible to recognize dikes of compact 

 greenstone cutting either coarser rocks of the same sort or siliceous 

 schists. 



The petrographical examination of the rocks failed to show that 

 they had occurred as surface flows, all of the characteristics being 

 those of intrusive rocks. The only possible exceptions are certain 

 rocks near the eastern border of the greenstone area. They are con- 

 siderably altered and have been mashed, and their field appearance 

 suggested that they were flow-breccias or tuffs, with fragments or 

 drawn-out lenses of greenish porphyry lying in a dense cementing 

 material of a darker color. Unfortunately, decomposition has pro- 

 ceeded too far for a microscopical examination to be of value ; second- 

 ary minerals are about the only ones that can be made out, but the 

 texture suggests crushing or mashing. The occurrence of these rocks 

 seems to be restricted to the region immediately adjoining the con- 

 tact with the Algonkian conglomerates, where, as has been said, 

 complicated infolding and fracturing have taken place, and it is more 

 reasonable to suppose that these rocks are friction breccias, subse- 

 quently mashed, than that they are of pyroclastic origin. 



