108 THE ROYAL SOCIETY OF CANADA 



limestones of this upper division may be of Cambrian age, at all 

 events older and not newer than the rocks, intrusive granite, diabase, 

 etc., which constitute the bulk of the lower division, thus doing away 

 with the existence of all Pre-Cambrian rocks in the St. John district. 

 To this view the authors of this paper find it impossible to accede. 

 For the fact that some of the limestones of Charlotte County, distant 

 some fifty miles from the region under discussion, have been found 

 to be Silurian rather than Laurentian, as was at one time conjectured, 

 does not prove that those of St. John are also Silurian, while a variety 

 of facts tend to show the contrary. The limestones of Charlotte 

 County are of very limited extent, they do not, like those of St. John, 

 alternate repeatedly with heavy beds of quartzite, nor are they, as at 

 St. John, directly overlaid by fossiliferous Cambrian strata. The St. 

 John limestones, etc., would appear, like the Grenville Series of Ontario, 

 to occupy narrow synclinaltroughsin the lower division of the Pre-Cam- 

 brian, though penetrated in part by granite batholiths of the latter, as 

 well as by numerous dykes which also penetrate the later Huronian strata. 

 In character also they bear much resemblance to the rocks of the 

 Grenville series, but as the exact position of the latter in the Pre- 

 Cambrian succession is itself still a matter of debate, no positive 

 correlation between the two is possible. The evidence, however, 

 of a Pre-Cambrian origin is as strong in the one case as in the other. 



(2) and (3) To answer these questions some reference must first 

 be made to another group of rocks which, about St. John, intervened 

 between those already discussed and the fossiliferous Cambrian. 

 They are those to which the term "Huronian" was applied in the 

 Geological Survey Report of 1870-71, but which in the Geological 

 Survey Map are designated simply as Pre-Cambrian. They were 

 subdivided by the present writers into two groups, of which the lower 

 or Coldbrook Group was described as mainly composed of volcanic 

 and semi-volcanic rocks, while the second or Coastal Group consisted 

 mainly of clastic rocks (chloritic and hydro-mica schists, slates and 

 conglomerates, with some limestones) though also including many 

 beds of igneous origin. 



Where these supposed Huronian rocks are exposed at St. John 

 they have but an insignificant thickness, being only about thirty feet 

 at the Suspension Bridge, and embrace only the lower or Coldbrook 

 division, but widen rapidly to the eastward, where the so-called 

 Coastal rocks occupy a very large area. Where, as at St. John, the 

 Coldbrook rocks are directly overlaid by the basal Cambrian, no 

 doubt can be entertained as to their true position and the same is the 

 case about the Loch Lomond Lakes, some few miles 'eastward, where 

 they enclose a trough or syncline of richly fossiliferous Cambrian beds, 



