[hahvie] palaeozoic BRECCIA OF THE VICINITY OF MONTREAL 253 



interior of He Jesus from whence an extension recrosses to the Island of 

 Montreal along the anticlinal mentioned above. 



Calciferous. — The Calciferous is a transitional stage between the 

 Potsdam sandstones and the limestones of the Chazy and Trenton. It is a 

 granular magnesian limestone or dolomite of a very compact nature. It 

 is found well developed on the west end of the Island of Montreal, also 

 lie Bizard. It occurs on He Jesus and occupies a very large area on the 

 mainland to the north. 



Potsdam. — This formation consists of fine grained, yellowish-brown 

 to white, very evenly bedded sandstone, with well defined vertical joint- 

 ing. In composition it is almost pure quartz. This formation is foimd 

 en the islands and west shore of Lake St. Louis, the southwest shore of 

 the Lake of the Two Mountains, and also on the northwest shore as a 

 belt surrounding the Laurentian outlier of the Oka Mountains. 



Pre-Cambriax. 



Anorthosiie. — This forms a small area near Cartierville, and is 

 identical with the anorthosite found intruding the Laurentian gneisses 

 and limestones in the Archsean district to the north. The probability is 

 that this occurrence once existed as a mountain peak in a Laurentian 

 country, which country, except for this isolated instance has since been 

 covered by the sediments of the St. Lawrence plain. 



An outlier of typical Laurentian gneiss, associated with a small 

 patch of crystalline Grenville limestone forms the mass of the Oka 

 mountains. 



Intrusives. 



Monteregian Hills. — As has already been briefly stated, the Monte- 

 regian Hills are the roots or remnants of an old system of volcanoes. 

 These hills, locally called " mountains " are eight in number their names 

 being : — Mount Eoyal, Montarville, Belœil, Mount Johnson, Kougemont, 

 Yamaska, Shefford and Brome. They stand " pretty nearly in a straight 

 line " running approximately east and west, over a distance of fifty miles. 

 To be rather more exact, six of the mountains may be considered as 

 situated either on a single straight line with a rather sharp curve in the 

 middle; or as on two shorter straight lines, each with three mountains, 

 which diverge from one another at an angle of about 30°, Montarville 

 being situated at the point of intersection. Mount Johnson and Brome 

 Mountain might then be considered as situated on short subsidiary frac- 

 tures. It is highly probable, in view of this distribution, that these 

 ancient volcanic mountains are, as is usual in such occurrences, arranged 

 along some line or lines of weakness or deep seated fracture. 



