TYPICA L LA URENTIA N A RE A OF CANADA. 329 



value, is of especial significance. This mineral which is not 

 found in the Fundamental Gneiss, occurs usually in little dissem- 

 inated scales but occasionally in veins. The limestones are 

 thoroughly crystalline, generally somewhat coarse in grain and 

 often nearly pure. They usually, however, contain grains of 

 serpentine, pyroxene, mica, graphite or other minerals, of which 

 over fifty species have been noted. They are often interstratified 

 in thin bands with the gneiss, in places are very impure, and 

 may be traced for great distances along the strike, being 

 apparently as continuous as any other element of the series. 

 This development of the Laurentian is known as the Grenville 

 Series, and has been considered by all observers to be above and 

 to rest upon the Fundamental Gneiss. In it are found all the 

 mineral deposits of economic value — apatite, iron ore, asbestos, 

 etc., which occur in the Laurentian. The rocks of this series, 

 though generally highly inclined, over some large areas lie nearly 

 horizontal or are inclined at very low angles, but even in such 

 cases they show evidence of having been subjected to great 

 pressure, resulting in some cases in the horizontal disruption of 

 certain of the beds. 



The areas occupied by the Grenville series although of very 

 considerable extent, being known to aggregate many thousand 

 square miles, are probably small as compared with those under- 

 lain by the Fundamental Gneiss. The relative distribution of the 

 two series has not been ascertained except in a general way in the 

 more easily-accessible parts of the great Archean Protaxis. The 

 Grenville series is known to occupy a large part of its southern 

 margin between the city of Quebec and the Georgian Bay, while 

 the discovery of crystalline limestone in the gneiss elsewhere at 

 several widely separated points, as for instance on the Hamilton 

 River in Labrador, in the southern part of Baffin Land and on 

 the Melville Peninsula, makes it probable that other considerable 

 areas will, with the progress of geological exploration, be found 

 in the far north. Over the greater part of the Protaxis, how- 

 ever, the more monotonous development of the Fundamental 

 Gneiss seems to prevail. 



