THE FORTIETH PARALLEL SURVEY. 501 



characteristics were not the result of any previous study, but solely of 

 the investigation of these particular rocks. Since Professor Zirkel 

 never studied the rocks of the Fortieth Parallel Survey in the field, and 

 since these diagnostic characters were obtained from those rocks only, 

 how was it possible for him to know which were nietamorphic, which 

 older eruptive, and which younger eruptive granites 1 



Mr. King states that the supposed Archjcan rocks were proved to 

 be of that age, not only by their lithological characters, but also by 

 their being seen in contact witli the Potsdam and some presumably 

 Cambrian rocks. These contacts were not within the limits of the For- 

 tietli Parallel Survey, and he gives us no information in regard to their 

 characters. (I., p. 21.) 



Mr. Hague's statement, however, goes to show that in point of fact 

 these rocks were upheaved in some parts since the Triassic ; in others, 

 since the Jurassic; and in others, since the Cretaceous (II., pp. 6-93). 

 This demands that one of two theories should be adopted ; either that 

 these rocks were pushed up in a solid body, or that they were erujjtive. 

 In the former case, they are regarded as ancient land bodies, about 

 which the later formations were deposited, all being subsequently up- 

 lifted by the granite upthrust. We fail to find any evidence in the 

 publications of the Survey that examinations were made to see if the 

 later formations {except the Tertiary and Cretaceous) contained debris 

 from the supposed Azoic (Archaean) ; or to ascertain whether the con- 

 tacts were those of one rock laid down upon another, or eruptive, 

 or such as would naturally occur in case a solid mass was thrust up 

 through another. In fact, no evidence in regard to these points is 

 adduced, except the statement that the supposed later formations lie 

 luiconformably against the Archaean, which unconformability would ex- 

 ist in any of the before-mentioned cases. Had evidence been seen, we 

 caiuiot imagine it would have been passed over in silence. So far as 

 this district is concerned, the oldest rocks in contact with the granitic 

 rocks are of Carboniferous age. Tiie supposed Azoic rocks are con- 

 siderel to be I.aurentian on the strength of lithological resemblances, 

 and they are also said to constitute one formation. In the district in 

 question, however, it is impossible to prove them to be older than the 

 Carboniferous ; and by neglecting to give the evidence, if any existed, 

 they are not shown to be older than the beginning of the Cretaceous. 

 (I., p. 299.) 



The gabbro of this range, which, according to Dr. Hunt, has the char- 

 acters of the Norian (Proc. Bost. Soc. Nat. Hist., 1878, XIX., p. 2 70), 



