﻿Pre- Cambrian Fossils especially in Canada. 159 



•Doubt has, however, been cast on these in a recent paper 

 by Dr. llauff, of Bonn. It is not improbable that the 

 Huronian may admit of sub-division into two members ; 

 and, if its deep sea limestones could be found, perhaps 

 into three. It underlies the Etcheminian unconformably, 

 and, so far as known, is itself unconformable to the 

 Laurentian, which must have been subjected to some 

 'disturbance and to much intrusion of igneous matter, as 

 well as to great denudation, before and during the 

 Huronian period. 



Next in descending order is the Upper Laurentian, 

 or G^envillian system (the upper part of Logan's Lower 

 Laurentian), which is well developed in the St. Lawrence 

 and Ottawa Valley and also in New Brunswick, as well as 

 in the Adirondacks and the eastern slope of the Apalachians. 

 It contains various gneissose and schistoze rocks, which, 

 though crystalline, show, on analysis, the same composition 

 with Palaeozoic slates,^ and it includes also bands of 

 quartzite and of graphite and graphitic schist, as well 

 as large beds of magnetite. Above all, it is remarkable 

 for the occurrence of great zones or belts of limestone, 

 associated with what seem to be altered sedimentary beds, 

 and is in many places rich in graphite and in apatite. It 

 is scarcely possible to doubt that in this great system of 

 several thousands of feet in thickness we have evidence of 

 tranquil oceanic deposition and of abundant animal and 

 vegetable life. It, no doubt, also occupies great areas 

 covered by later deposits, while there is evidence that the 

 portions exposed have undergone enormous denudation. 



The graphite of this system has yielded no distinct 

 structures, except imperfectly preserved fibres ; but in 

 some places it assumes the form of long ribbon-like bands, 

 suggestive of fronds of algte, and an American palaeontolo- 

 gist, Mr. Britton, has described one of these forms from 



1 Adams— Am. Journal of Science, July, 1895. 



