OF CENTRAL CANADA PART III. 



185 



tended line of fissure. The picturesque mountain of Montreal, and 

 the mountains of Beloeil, Monnoir, Rougement, &c., are examples. 

 These salient masses exhibit in places a distinctly conical or partly 

 truncated form, as seen in the outline of the "Paps," (Fig. 103), on 



the east side of Black Bay, Lake 

 Superior, and to some extent, 

 also, in many of the greenstone 

 hills of the Eastern Townships. 

 A step-like and more or less 

 tabular outline, as already re- 

 FIQ. 103. marked, is likewise very charac- 



teristic of rock masses of this group. 



The variable composition and diversities of structure exhibited by 

 trappean rocks have given rise on the part of lithologists to the 

 formation of a great number of so-called species, each provided with 

 a distinct name, usually of Greek derivation. But these attempted 

 distinctions are in many instances of purely local application ; and 

 in very few cases can they be regarded as indicating definite admix- 

 tures of ready recognition. Names applied to particular varieties by 

 one author, are applied quite differently by others. The terms 

 melaphyre, porpLyrite, diabase, &c., might be cited as examples. In 

 many cases also, the same rock, if presenting slight differences of 

 texture, or if assumed, without any possibility of proving the assump- 

 tion, to contain augite in one case and hornblende in another, is 

 described under different specias. In this manner, fanciful distinc- 

 tions which have no true foundation in Nature, and which cannot 

 be rigorously or definitely applied, are attempted vainly to be 

 carried out in many so-called systems of lithology. If minute 

 chemical or mineralogical differences were regarded as essential, 

 our Canadian varieties of this group of rocks might add many 

 names to the already uselessly extended list. It is not possible 

 however in the present state of the question, nor is it desirable 

 in an elementary work of this character, to depart altogether 

 from the beaten track. Retaining therefore some of the more gene- 

 rally recognised names and distinctions, whilst duly admitting the 

 more or less arbitrary and uncertain character of these, we may refer 

 our Canadian rocks of the Trappean series to the following varieties : 

 (1) Trap or Basalt; (2) Dolerite or Granitoid Trap; (3) Greenstone 



