ROCKS OF THE ATLANTIC COAST OF CANADA, ETC. 799 



any case afford better means of comparison with theLaurentian of other 

 districts, and the occurrence of masses of binary granite and syenite 

 in the Lower group and of labradorite in the Upper need not inter- 

 fere with such comparisons, though it is to' be observed that in the 

 Upper member plagioclase felspars are much more abundant than in 

 the Lower. Prof. Bonney has some very judicious remarks on this 

 in his Anniversary Address before this Society in 1886. 



Whatever views may be entertained as to the origin of these old 

 rocks, no one who has studied the typical districts of the Ottawa 

 Kiver can doubt for a moment that they are regularly bedded de- 

 posits, and that in the middle Laurentian those conditions which in 

 later periods have produced beds of limestone, sandstone, iron-ore, 

 and even of coal, were already in operation on a gigantic scale *. 

 At the same time it may be admitted that some areas of the lower 

 gneiss may be cooled portions of an original igneous mass, and that 

 many of the schistose rocks may be really bedded igneous materials. 



Turning now to the Atlantic coast, the greatest area of Lauren- 

 tian rocks is that forming the nucleus of the Island of ^Newfoundland. 

 In the northern part of that island the absence of the great crystal- 

 line limestones would seem to indicate that the lower member of the 

 series alone is represented. The same remark applies to the contin- 

 uation of the formation in the south of the island, with the exception 

 that indications of graphitic limestone and of magnetic iron-ore have 

 been found in two places f. 



It is to be noted here that the great uplift in Pre-Cambrian times of 

 the Laurentian nucleus of Newfoundland seems to have acted as an 

 outwork to the formations to the westward, protecting the area of 

 the Gulf of St. Lawrence from those thrusts from the eastward 

 which have piled up in gigantic earth- waves the older formations of 

 other parts of Eastern Canada and the Appalachian region. In con- 

 sequence of this the area of the Gulf of St. Lawrence has throughout 

 Palseozoic time remained undisturbed, and has conformed in its con- 

 ditions of deposit rather to the internal plateau than to the maritime 

 districts. 



In Cape Breton the isolated mass of St. Ann's Mountain seems to 

 be a representative of the Lower Laurentian of Newfoundland, and 

 Mr. Fletcher's observations render it probable that rocks of this kind 

 exist in the northern extremity of the island. In Nova Scotia proper 

 I have not been able to recognize any true Laurentian, the rocks 

 attributed by some other observers to this age being, in my judgment, 

 intrusive granite masses of much later date associated with altered 

 rocks t. 



In southern New Brunswick, however, the Laurentian reappears. 

 As seen near St. John, the lower part consists of red and grey gneiss 

 with chloritic gneiss and diorite. The occurrence of hydrated silicates 



* Q. J. G. S. vols, xxiii., xxv., xxxii., xxxv. In these papers I have set forth 

 not merely the evidence for the organic character of Eozoon, but for that of 

 the Laurentian limestones and graphites and phosphates in general. 



t Murray's ' Geol. Survey of Newfoundland,' 1881. 



\ Supplement to Acadian Geology, 1878, p. 89. 



3g2 



