On the Norian or " Upper Laurentian " Formation. 1*73 



of bituminous and carbonaceous substances which we find 

 filling cracks and fissures in bituminous and carbonaceous 

 beds in more recent formations. But the chief bulk of the 

 graphite occurs finely dissiminated through the rocks as 

 above mentioned. 1 



It was, however, observed by the geologists who first 

 worked on these Laurentian rocks that there occur, in many 

 places together ' with the above mentioned orthoclase 

 gneisses, &c, great areas of a rock that is principally and 

 sometimes almost exclusively composed of a triclinic or 

 plagioclase feldspar. They found that in many places the 

 structure and the appearance of this rock varied consider- 

 ably from place to place ; it being sometimes massive, 

 sometimes schistose, sometimes coarse grained, sometimes 

 fine grained. But all these structural varieties agree in 

 having the same composition. 



For this reason they were all placed tegether in one class 

 and called " Anorthosite Rock " or " Anorthosite,'' a name 

 derived from " Anorthose," a term proposed by Delesse to 

 designate the triclinic feldspars, and which is thus synony- 

 mous with the term "Plagioclase" now more commonly 

 employed. This designation therefore serves to emphasize 

 the difference between these and the predominating ortho- 

 clase feldspar rocks of the rest of the Laurentian. 



The term " anorthosite " which has been often misunder- 

 stood 2 on account of its presumed derivation from anorthite, 

 a feldspar which rarely occurs in these rocks, has hitherto 

 found no place in the systems most generally used in the 

 classification of eruptive rocks. But in Canada, it has been 

 used for many years, and will here be employed to designate 

 a certain well defined class of rocks which belong to the 

 family of gabbros and which stand at one end of the series, 

 being distinguished by the marked predominance of plagio- 

 clase and the marked subordination or entire absence of all 

 coloured constituents. Their place in the family of gab- 

 bros, corresponds in a certain way to that of the pyroxenites 



1 For further evidence see Sterry Hunt, Chemical and Geological Essays, p. 272, 

 and Sir William Dawson : " The Dawn of Life " and many other writings. 



2 Wichman, Zeit. der Deutsch. Geol. Ges., 1884 p. 496. 



