798 SIE J. W. DAWSON ON THE EOZOIC AND PALEOZOIC 



I. The Latjeentian System. 



It is, I think, becoming more and more evident that in every 

 part of the world the oldest rocks exposed are of the nature of ortho- 

 clase-gneisses associated with various kinds of crj'stalline schists, 

 and locally with quartzites and limestones. This statement applies 

 with equal force to the Acadian Provinces of Canada and to west- 

 ern Europe. In these districts, however, the old Laurentian sub- 

 stratum is represented, not by great continuous areas, as in the 

 interior of North America, but by rugged islets and ridges of 

 cr5'stalline rock, in most places so imperfectly exposed that their 

 subdivisions can scarcely be made out, and that geologists may even 

 be excused for doubting the stratified character of their rocks. It 

 is only by comparing them with the magnificent series exposed in 

 the country north of the St. Lawrence, and worked out so ably by 

 Logan, that the more limited exposures of the Atlantic margins can 

 be understood. 



In the Journal of this Society for February 1865 will be found a 

 summary statement by Logan of the structure of this formation, which 

 still holds good*. He there divides the Laurentian into two series, the 

 lower and the upper, the former largely composed of othoclase-gneiss, 

 but with beds of limestone, quartzite, and micaceous and hornblendic 

 schists in its upper parts ; the latter composed of similar gneisses 

 and limestones, but with beds of gneissose anorthosite and lab- 

 radorite, and great masses of coarsely cleavable labradorite and 

 hypersthene. 



It is perhaps unfortunate that these last masses, many of them, no 

 doubt, accidental and intrusive, so forcibly attracted the attention of 

 Logan that he characterized the upper Laurentian as a labradorite 

 series, whereas the true aqueous rocks of this series would afford 

 better terms of comparison with other districts than merely igneous 

 masses or beds. A similar objection, I think, applies in some degree 

 to the name Norian, as more recently given by Hunt ; and I have no 

 doubt, from my own observations in the typical districts, that Logan's 

 division must stand, though perhaps it would be well to separate the 

 lower gneiss from the remainder of his Lower Laurentian and to re- 

 cognize a Lower, Middle, and Upper group, all of which are distinctly 

 crystalline rocks t. The upper member, as developed in the west, should, 

 I think, include some of the crystalline rocks which have been classed as 

 Huronian, and which seem to fill part of the gap between the latter and 

 the Lower Laurentian in the regions further east J. This view will in 



* " On the Eozoic and Palaaozoic Eocks." 



t The two principal members have been named respectively the Ottawa and 

 Grenville series. The third, or upper member, in Logan's typical district has 

 been separated as the Norian series by Hunt ; and by Selwj-n (Reports Greol. 

 Survey of Canada, 1879-80) is regarded as mainly composed of igneous rocks. 

 In the maritime Provinces, as we shall see, only two members have been recoo-- 

 nized. 



+ Dr. Bigsby, " On Lake of the Woods," Journal of Geol. Society, 1851-2 ; Dr. 

 G. M. Dawson, Eeport on 49th Parallel, 1875 ; Mr. Lawson, Eeports Geol. 

 Survey of Canada, 1885. The latter has proposed the name " Keewatin" for 

 some of these rocks in the west. 



