THE MONTEREGIAN HILLS 253 



that the flat-lying strata all about it are not arched up, but abut 

 sharply against the igneous core of the mountain and are cut off 

 by it. Being shales, they are of course baked to hornstones, 

 but show no signs of upheaval or tilting. The small size and 

 almost circular cross-section of the mountain are a further indi- 

 cation 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 Professor Davis, 

 in his Physical GeograpJiy , from one of the author's photographs, 

 as a typical example of a volcanic neck. 



In a recent paper by Buchan^ the view was put forward that 

 Mount Royal 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 sedimentary strata of the plain 

 from which the mountain rises. This alone, however, is not 

 suf^cient to establish a laccolitic 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 mountain, 

 they abut against the intrusive rock and are cut off by it instead 

 of being uptilted, 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 cer- 

 tain 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 laccolitic structure 

 for the mountains as a whole, or that the igneous material did 

 not find a vent at the surface, there developing a volcano. In 

 fact, there is evidence in the existence of a remarkable deposit 

 of a breccia-conglomerate in several places around the mountain 

 that it did develop as a volcano and that the materials constitut- 

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

 this breccia was undertaken last autumn by one of the geological 

 field parties of McGill University, and a description of it, with a 



' Canadian Record 0/ Science, Vol. VIII (1901), p. 321. 



