22 THE BRIAN, OU DEVONIAN. 



in such circumstances as prove the later date of the latter, and there 

 are now in my collections specimens showing the gradations from 

 the fossiliferous to the altered strata, including some which hold 

 Oriskany fossils, but have assumed an incipient gneissic structure, 

 and were penetrated by granite veins. It is further to be observed 

 that the age assigned by me to these granites accords with the fact 

 that in Nova Scotia the formations older than the Carboniferous are 

 more or less in an altered and disturbed condition, and that granite 

 debris does not occur as a prominent ingredient in our formations till 

 the Lower Carboniferous age. In the district in question, the thick 

 beds of granitic sandstone in the Lower Carboniferous near Wolfville 

 and Lower Horton afford a good illustration. Besides this, we have 

 to consider the evidence given in the body of this work of the age of 

 similar granites in other parts of Nova Scotia, and referred to above. 



I should add here that the age above claimed for a portion of the 

 Nictaux series in no respect conflicts with that assigned in 1860* 

 by Prof. Hall and myself to the Silurian iron ores of the East River 

 of Pictou, and illustrated at page 594, and First Supplement, page 76, 

 and in my paper of 1880. -j- These are somewhat older than the 

 ferruginous beds of Nictaux, being of Lower Helderberg age, and 

 apparently associated with strata still lower in the Silurian series, 

 and some of which are probably synchronous with the Lower Arisaig 

 (Clinton) series. 



In Pennsylvania bedded iron-ore deposits occur in the Clinton, 

 Lower Helderberg, Oriskany, Corniferous, and Marcellus, so that they 

 range, as I believe they do in Nova Scotia, from the Middle of the 

 Upper Silurian to the Lower Devonian inclusive. | The principal 

 deposits in Pennsylvania are in the Clinton, Oriskany, and Marcellus. 

 In Nova Scotia only small layers are known to me, at Arisaig and 

 East River, so low as the Clinton, and the principal deposits seem to 

 be Lower Helderberg and Oriskany, The analogy is thus sufficiently 

 close, beds of the age of the Marcellus not having been recognised 

 in Nova Scotia. 



V. THE SILURIAN. 



In the inland plateau of North America this period begins with 

 shallow-water conditions passing into the great and long-continued 

 depression marked by the Niagara Limestone. There is then a second 

 elevation, that of the Salina, succeeded by the very widely distributed 



* Canadian' Naturalist, vol. v. 



f Ihid., vol. ix. 



X Second Survey of Pennsylvania, vol. F. 



