THE SOUTHERN COMPLEX. 1 1 3 



ever, large and f^mall complex areas liaving the appearance both macroscop- 

 ically and microscopically of an ordinary granite are contained in a matrix of 

 exceedingly finely crystallized material. If this difference in the character of 

 the coarse and fine parts is taken to mean that the coarser part crystallized at 

 depth and the latter after a change of condition and near the surface, the con- 

 clusion would be that the crystallization had proceeded much further than 

 usual in porphyries before the change in condition occurred. And, if this is 

 so, the specimen throws some light upon the manner of crystallization of 

 granites. In the development of the minerals in massive igneous rocks, it is 

 usually assumed that the crystallization of the different species is in the main 

 successive, although to some extent simultaneous. It would apjjcar that in 

 this rock, wliile this ma}' be to a small degree true, it is certain that l)efore 

 the change of condition occurred all of the minerals found in a granite had 

 begun to develop, and in such a fashion as to make small masses of perfect 

 granite. These masses of granite, associated with simple individuals of 

 quartz and feldspar, were separated from each other by the liquid magma 

 in which thev were contained. After the chaufje of conditions the magma 

 rapidly crystallized, tlius preserving the individuals and clusters of individ- 

 uals ^^hich liad l)efore formed. If the growth had continued without a 

 change of conditions, the simple and complex areas would ])robably have 

 formed larger and larger masses of granite until the whole space was occu- 

 pied. This implies that in the outward growth of each mass all of the min- 

 erals which go to make up a granite separate from a magma in which these 

 same minerals have before developed in such relations to each other as to 

 have for short distances the typical structure of a deep seated crystalline 

 rock. This manner of growth differs radically from tliat first mentioned as 

 the ordinary conception of the crystallization of igneous rocks. 



The exposures west of the Montreal river, and a few of those a short 

 distance east of it, are of a more liasic character than the gi-anites. The 

 rocks here included are syenites and gabbros, the latter being nuich altere(l. 

 The granites east of the Montreal differ in acidity. In content of (piartz 

 they vary from a normal rock to one in which the quartz is distinctly 

 subordinate to the other constituents, and which might with equal pro- 

 priety be classed as a granite or a syenite. The syenites west of the Mon- 

 JJON jtix 8 



