462 STRATIGRAPHICAL GEOLOGY. 



north-west direction, near the village of St. Helene, the wide-spread alluvium of the 

 St. Lawrence valley is reached, occupying an area of several thousand square miles, in 

 which very few rock outcrops are observed. This area is said to be underlaid by the 

 Utica and Hudson river formations, which again are said to overlie conformably the 

 Trenton and Chazy limestones, and the Calciferous and Potsdam sandstones. All 

 these rocks form part of a series of sedimentary strata occupying certain areas in the 

 valley of the St. Lawrence, lying horizontally or nearly so, and supposed to be of Lower 

 Silurian age. The Potsdam sandstone is the lowest member of this group of strata, 

 and is regarded as the oldest Silurian rock, and possessing even greater age than the 

 mica schists and clay slates of the eastern townships. Indeed, in the attempts which 

 have been made at determining the age of the latter rocks, it has always been the rule 

 to begin with the Potsdam sandstone as the oldest rock, and to assume that those to 

 the eastward (regardless of their lithological characters) followed each other in ascend- 

 ing order. Any one who has studied the structure of similar regions in Europe, such 

 as those above mentioned, can scarcely fail to come to the conclusion that the opposite 

 of this assumption is the truth ; that the oldest rocks are those of New England, and 

 that, as we come north-westward, we pass over more and more recent strata. This 

 view would be maintained in spite of the prevailing dip to the south-eastward, which 

 can only be accounted for by assuming, with Emmons, that the strata have been over- 

 turned, — this, and indeed the plications of the whole series, having been caused by 

 some enormous pressure from the south-east. 



" In distinguishing the Green Mountain series. Dr. Hunt seems to have been unable 

 to leave the beaten track, in which he had previously travelled, and to regard the more 

 eastern crystalline rocks as the older instead of the newer. He still adheres to the 

 idea that the Green Mountain rocks, because they apparently underlie the White 

 Mountain mica schists, etc., are the older rocks. In referring to the Laurentian sys- 

 tem, it has been shown how entirely inconsistent with European experience this sup- 

 position is. 



" In the preceding section the opinion has been expressed that Dr. Hunt has gone too 

 far in asserting the pre-Cambrian age of the Green Mountain schists. In maintaining 

 their pre-Silurian age, however, he merely adopts a view advocated by myself as early 

 as 1862. In describing the Dovrefjeld slates, and comparing them with similar rocks 

 in the Quebec group and Green Mountain series, I made the following remarks : 

 ' Different views prevail, as to their age, in different countries. In Cornwall they are 

 considered Devonian ; in Scotland, Lower Silurian ; and in Bohemia, as in Norway, 

 pre-Silurian, In Belgium, Rhenish Prussia, Westphalia, and Nassau, they are by some 

 geologists regarded as Devonian, and by others as belonging to an older formation. 

 In East Russia, on the western slope of the Ural Mountains, they are supposed to 

 represent Lower Silurian strata. A dissimilarity of views will probably continue to 

 prevail as to the position of these rocks until the question is decided as to what value, 

 in the absence of fossils, the petrographical characters o'f a group, taken in connection 

 with its stratigraphical position, should have in determining its age. Perhaps there 



