322 Canadian Record of Science. 



have some value, even although it falls far short of meet- 

 iag the whole question. 



In approaching the subject, there is great difficulty in 

 arriving at a just appreciation of the conditions which 

 prevailed in that immensely distant age before the moun- 

 tain arose from the depths below. If we attempt to 

 reason from tlic conditions of the present, we will find but 

 little to assist, and much to mislead, and it is only when 

 all the facts relating to the different conditions which 

 have prevailed, and tlie changes and vicissitudes through 

 which the earth has passed are brought together, and their 

 relation to and bearing on each other are given due 

 weight, that any correct idea of these things can be 

 formed, and the possible liistory of the mountain in some 

 measure understood. 



Mount Royal is an intruded mass of trap, which has 

 been forced upward through an opening or fracture in the 

 lower Silurian strata by which the whole country in the 

 neighborhood of Montreal was overlaid. 



The first point to be noticed is that the limestone strata 

 befng pierced by the trap, it necessarily follows that the 

 eruption must have occurred after it was laid down. This 

 affords a means of approximately fixing the period at 

 which the eruption occurred, or, at least, of knowing it 

 could not have occurred until after a certain period had 

 elapsed. 



On the other hand, as we shall see, it must have taken 

 place before the time of the Lower Helderberg group. 

 Which is the highest member of the Upper Silurian forni- 

 ati'on.' 



■At various places, almost to the top of the mountain, 

 fragments of the Lower Silurian strata are found, 

 apparently in place, where they have been protected from 

 erosion by the harder trap rock. 



From this it would appear that the overlying strata 

 have, to a great extent, been removed by denudation, that 



