R. A. Daly — Mechanics of Igneous Intrxision, 119 



understanding of the Madoc and Marmora District as a fine 

 example of contact-shattering by an eruptive. The zone on 



my map ' ' ^ , , is preeminently a zone of apophyses, 



these being very numerous, running in every direction, more 



numerous than elsewhere (except in the zone * A "R '^ 



and being mostly fine-grained granite with little or no mica . . . 

 Both zones form decidedly a zone of strong shattering about 

 the intrusive, extending, to a less degree, beyond, all around it, 

 as shown by the separate granite masses and dikes marked 



(and many not marked) on the map The typical 



granite of that intrusion is a rock of medium-size grains of 

 reddish orthoclase and of round, blue quartz with a little mica, 

 but this passes into a great variety of other rocks." 



Mr. Coste holds that there has been some chemical modifica- 

 tion of the magma in the zone of inclusions by the incorpora- 

 tion of the limestone and calcareous schists, but has given no 

 details on the evidence. 



Owing to the overlap of the Ordovician limestone lying 

 unconformably on both the Archean schists and the granite, 

 the whole story of the shattering cannot be made out at the 

 present land surface ; yet the exposure of the shatter-zone is 

 nevertheless remarkably instructive. The general aspect of 

 the map, the breadth of the zones, the existence of patches of 

 the invaded formation lying isolated in the largest stock, and 

 the numerous smaller bosses which occur like satellites about 

 the main granite body — all lead to the conviction that the 

 present erosion-surface is close to the position occupied by the 

 roof of the chamber when the magma of the largest stock was 

 solidifying. 



Illustration from the geological structure near Trail^ British 



Colmnhia. 



The second illustration of extensive shattering at granite 

 contacts is selected from the many that might be described 

 from southern British Columbia. The selection has been made 

 not because the phenomena are qualitatively different from 

 those to be seen about other molar contacts in the region, but 

 for the twofold reason that the shatter-zone has here been act- 

 ually mapped and that the zone is wide enough to be sketched 

 on a map of small scale. The area concerned is shown in fig. 

 2. It is seen to lie between the town of Trail and the lOth 

 Parallel Boundary with the United States. It is only a few 

 miles east of Rossland and for the most part on the right bank of 

 the Columbia River. This little sketch-map is based on the 

 *' Trail Sheet" issued by the Geological Survey of Canada 



