The Monteregian Hills. 213 



of upheaval or tilting. The small size and almost circular 

 cross-section of the mountain are a further indication of 

 this origin ; and finally there is conclusive proof that there 

 was a vertical or upward movement of molten rock 

 through the pipe. The mountain has been figured by Pro- 

 fessor Davis, in his Physical Geography, from one of the 

 author's photographs,as a typical example of a volcanic neck 

 In a recent paper by Buchan 1 the view was put forward 

 that Mount Eoyal represents the remnant of a denuded 

 laccolite — on the ground that on one side of the mountain, 

 toward the summit, there is an isolated mass of flat-lying, 

 altered Paleozoic limestone, evidently a part of the sedi- 

 mentary strata of the plain from which the mountain 

 rises. This alone, however, is not sufficient to establish a 

 laccolite origin, and opposed to such an explanation is the 

 fact that where the strata of the plain are seen along their 

 immediate contact with the intrusion in many places, 

 especially on the eastern and northern side of the moun- 

 tain, they abut against the intrusive rock and are cut off 

 by it instead of being uplifted, the igneous core of the 

 mountain rising up precipitously like a wall across the 

 truncated edge of the beds. The occurrences of the flat- 

 lying limestone on the side of the mountain referred to 

 above appear to represent the remnant of certain beds, 

 beneath which a portion of the intrusive mass penetrated, 

 after the manner of a laccolite, on one side of the mass. 

 Their existence does not by any means indicate a laccolite 

 structure for the mountains as a whole, or that the igne- 

 ous material did not find a vent at the surface, there de- 

 veloping a volcano. In fact, there is evidence in the 

 existence of a remarkable deposit of a breccia-conglomer- 

 ate in several places around the mountain that it did de- 

 velop as a volcano and that the materials constituting 

 the deposit in question were ejected from it. A study of 

 this breccia was undertaken last autumn by one of the 



1 Canadian Record of Science, Vol. VIII, [1901], p. 321. 



