

662 THE HURONIAN AND LAURENTIAN PERIODS. 



sider their precise position as uncertain, only remembering that they 

 constitute a series lower than the Primordial rocks, at the base of 

 the Silurian." 



The rocks of the lower part of the Coldbrook group being much 

 harder than those of the upper member, and than those of the St 

 John group, present a marked feature in the topography of the country, 

 projecting in a bold and rugged ridge, well marked for some distance 

 to the eastward of St John. 



The Huronian of Western Canada is rich in metallic minerals, more 

 especially in copper ; but that of New Brunswick has not as yet 

 afforded useful minerals. Indications of copper and lead, however, 

 occur in rocks referred to this age on the Hammond River, near 

 Quaco, and in other localities specular iron has been observed. 



It is to be observed that while on Lakes Huron and Superior the 

 lower Silurian rocks of about Chazy age rest unconformably on the 

 Huronian ; at St John, the Primordial shales of the Acadian group, 

 which are, however, much older than the Chazy, appear to repose 

 conformably on the Coldbrook series. 



Laurentian Series [Portland Group). 



Regarding the group of rocks last described as Huronian, there 

 seems no alternative but to assign the great mass of calcareous and 

 gneissose rocks underlying the Coldbrook group to the Laurentian. 

 These rocks form an anticlinal northward of the Coldbrook group, 

 and occupy an area about forty miles in length and from two to eight 

 miles wide. In the immediate vicinity of St John, they are overlaid, 

 apparently conformably, by the Coldbrook group. They may be ob- 

 served elsewhere to be covered unconformably by rocks of Devonian 

 and Carboniferous age. 



When examining these rocks several years ago, I was struck with 

 their resemblance to the Laurentian of Canada ; but as nothing was 

 then known with certainty as to the age of the St John rocks, I could 

 not venture to assign them to so ancient a period. Their mineral 

 character, as it then presented itself to me, is described as follows :* — 



" The oldest rocks seen in the vicinity of St John are the so-called 

 syenites and altered slates in the ridges between the city and the 

 Kennebeckasis River. These rocks are in great part gneissose, and 

 are no doubt altered sediments. They are usually of greenish colours ; 

 and in places they contain bands of dark slate and reddish felsite, as 

 well as of gray quartzite. In then- upper part they alternate with 

 white and graphitic crystalline limestone, which overlies them in 



* Journal of Geological Society, vol. xviii. 



. 



