428 Canadian Record of Science* 



V. AGE OF THE ANORTHOSITE INTRUSIONS AND 

 THEIR RELATION TO THE MARGIN OF THE 

 ARCH.EAN PROTAXIS. 



The North American Continent, as is well known, is 

 bnilt up around a skeleton or nucleus of crystalline rocks,, 

 called by Dana the protaxis of the continent, and by 

 which the general outline of the continent is defined.. 



The most important portion of this protaxis is the large 

 area of Lauren tian, together with the Huronian, which lies 

 almost entirely within the boundaries of the Dominion, 

 forming the " Canadian shield," with the bordering ranges 

 of the coast of Labrador. It is a large triangular area,, 

 whose sides, towards the south-east and the south-west, 

 form tangents to the arctic circle, and which, towards the 

 north, extends up into the polar regions far beyond the 

 limits of exploration, where, however, it is overlaid to a 

 considerable extent by more recent rocks, • A range of 

 these Archaean rocks extends likewise along the Atlantic 

 coast, where it appears, with certain interruptions, in the 

 Appalachian chain, extending from Georgia, in the United 

 States, to the Gaspe peninsula in Canada. It is succeeded 

 to the east by a second range, partly under water, and 

 portions of which are seen in Nova Scotia and elsewhere 

 along the Atlantic coast. Corresponding to these two 

 areas, there occur also, on the western side of the conti- 

 nent, nuclei of these old crystalline rocks, which appear 

 in the line of the Rocky Mountains and in the coast 

 Ranges. 



The greater portion of the main protaxis, as well as the 

 distribution of the Laurentian and Huronian rocks, with 

 that of the palaeozoic beds overlying them, are represented 

 on Map No. 1. The southern limit of the protaxis extends 

 westward beyond the map, and runs in a north-westerly 

 direction nearly as far as the Arctic Ocean, which it 



