THE MONTEREGIAN HILLS 249 



In addition to these bodies of intrusive rock which form the 

 mass of the mountains, great numbers of dykes occur cutting both 

 the surrounding sedimentary strata and the intrusions. These 

 are, of course, especially numerous in and around the mountains 

 themselves, but are also occasional!}' found far removed from 

 the centers of activity. The relative abundance of these dykes 

 in the vicinity of the several mountains varies greatly. They 

 swarm through the Paleozoic strata about Mount Royal, cutting 

 the limestones in all directions and also traversing, although 

 less frequently, the igneous rock of the main intrusion as well. 

 No less than twenty-nine dykes and flows, belonging to at least 

 four and possibly five separate series, each cutting the preceding 

 set, were mapped by Dr. Harrington some years ago in an exca- 

 vation measuring 220 yards by lOO yards which was opened up 

 in the Trenton limestone on the flank of Mount Royal during 

 the construction of the Montreal Reservoir extension. Dykes, 

 in fact, abound wherever in the vicinity of Mount Royal the bed- 

 rock is exposed by the removal of the mantle of drift, as for 

 instance at the Mile End Quarries, St. Helen's Island, and in the 

 bed of the St. Lawrence about Point St. Charles when it is 

 exposed at low water. The whole district about the city would 

 present a network of dykes, could the overlying drift be 

 removed. 



Dresser mentions dykes as occurring abundantly about Shef- 

 ford mountain. In Mount Johnson, on the other hand, they are 

 almost entirely absent. Only five dykes could be found after a 

 careful exploration of the whole occurrence, and they were of 

 insignificent dimensions. But very few dykes also occur at 

 Beloeil mountain. A large number of the dyke rocks have been 

 collected from the various occurrences and are now awaiting 

 investigation in the geological department at McGill University. 

 The work on the dykes of Mount Royal is now well advanced 

 and, it is hoped, will be ready for publication shortly. They 

 form a most remarkable series, comprising bostonites, tinguaites, 

 solvsbergites, camptonites, fourchites, monchiquites, and alnoites. 

 Most, if not all, of the types of dyke rocks which have been 

 described as occurrinar in association with the alkaline rich 



