54 



Canadian Record of Science. 



The position of these various exposures is shown on the 

 accompanying sketch map of the Montreal district, the 

 breccia being indicated by a triangle. 



Figure 2 



Sketch Map 

 Showing distribution of Breccia 



In working out the geological relations of the 

 breccia, the occurrence on St. Helen's Island being con- 

 sidered the most typical as well as the largest, has been 

 made the subject of a detailed study. The other ex- 

 posures have also been examined and correlated with that 

 of St. Helen's with the view of arriving at some general 

 conclusion which will satisfactorily account for the origin 

 and age of the breccia. 



General Geology. See map, fig. 1. Two geological 

 formations are represented on St. Helen's Island and 

 these have had a marked influence on the topographic 

 features. The south-west half of the island, underlain by 

 Utica shale, is low and level, while the north-east area; 

 underlain by breccia, is rolling and comparatively hilly 

 Both shale and breccia are cut by dykes and sills which 



