358 IE W. ELLS — LAURENTIAN OF THE OTTAWA DISTRICT. 



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in other places in large corrugations ; but in the upper part of the mass 

 these frequently disappear and the strike and dip can be readily seen. 

 Occasionally the subjacent gneiss is crumpled in a similar manner, but 

 this is not the case as a ride. In certain areas also the limestone mass 

 contains well-rounded pebbles or masses of quartzose rock and grayish 

 gneiss, presenting the aspect of a true conglomerate. This character can 

 be well seen in a low cliff one mile and a half in rear of Calumet station, 

 on the Canadian Pacific railway, as well as at many other points around 

 the shore of the inland lakes, conclusively showing that this conglom- 

 erate is widely distributed. 



Associated intrusive Rocks. 



In addition to the gneiss and limestone, which may be regarded as 

 forming the great mass of the Laurentian rocks, certain areas of intrusive 

 rocks present features which are worthy of something more than a merely 

 passing notice. Of these some are of large extent, as in the case of the 

 anorthosite areas north of Saint Jerome and the syenite masses of Gren- 

 ville and Chatham, while other masses, though not so conspicuous as 

 these, are equally important as having exercised a marked influence 

 upon the occurrence of the principal economic minerals of the district. 



Of these no less than six. if not seven, clearly distinguishable periods 

 of intrusion can be recognized. In addition to the large masses of anor- 

 thosite and syenite just referred to, presumably the large areas of 

 augen-gneiss seen more particularly in the country adjoining the upper 

 Rouge river belong to this class, since they have without doubt exercised 

 a marked effect upon the strike and dip of the gneissic and calcareous 

 rocks with which they are in contact. The masses of augen-gneiss pre- 

 sent no trace of stratification and very rarely even of foliation. 



Of smaller intrusions may be mentioned the great series of pyroxenic 

 dikes which penetrate the irneiss of the phosphate district, and which 

 are generally of some shade of green, and the quartz and feldspathic, 

 generally white-weathering, dikes which are also prominent in the same 

 area. Certain black, fine-grained trappean dike- are also frequent which 

 cut both the preceding, some of which can be traced for many miles 

 crossing the strike of both the gneiss and the limestone. In regard to 

 the age of these trappean dikes it may he said that while, they cut the 

 limestone transversely they are cut off by the mass of the Grenville 

 syenite. 



In connection with this syenite also is a mass of intrusive porphyry, 

 evidently from the mode of its occurrence of later date. Other smaller 

 intrusions, but recognized at points over a very wide area, are of a very 

 coarse, black hornblende rock, in which the hornblende is the chief 



