AMERICAN GEOLOGY THE TACONIC QUESTION. 



669 



thirteen years a great revolution of opinion had come about; and that 

 the idea that the rocks of the Taconic system were really above the 

 Potsdam sandstone (as had been contended) had been exploded. (See 

 letter to Meek quoted above) 



As he understood the matter at the time of writing, some of the 

 Taconic rocks were certainly more ancient than the Potsdam, while 

 others might be of the same age, and perhaps some of them more 

 recent. The details, he felt, had not yet been worked out, and on 

 account of the extremely complicated structure of the region, he ven- 

 tured to say that no man at that time living would ever see a perfect 

 map of the Taconic region. The present indications are favorable to 

 this view of the subject. 



The theory that the Taconic rocks belong to the Hudson River 

 group, he went on to say, was an w * enormous error"' that originated 

 in the geological survey of New York and thence found its way into 

 the Canadian survey. The mistake was 

 doubtless due to the extraordinary arrange- 

 ment of the rocks, the more ancient strata 

 being elevated and often shoved over the 

 more recent, so that, without the aid of 

 paleontology, it was impossible to assert 

 positively that they were not the age of the 

 Hudson River formation, as they appeared 

 to be. The main object of his note was ac- 

 knowledged to be, to show that while the 

 error had originated in New York, it was 

 corrected by thegeologieal survey of Canada. 



This article brought out a reply by J. D. 

 Dana in the American Journal of Sci- 

 ence for June, 1872, in which he called 

 Billings's attention to the fact that, while he, Dana, might differ 

 with Billings about the Taconic, the differences, after all. were not 

 material, since Billings viewed the Taconic as developed by Emmons 

 through successive interpolations year after year, and not as first 

 announced in 1842. He called his attention, further, to the fact that 

 the system was based on a section fifteen miles long, made across the 

 Taconic Range, through Williamstown and Grevlock, to North Adams 

 on the east and to Petersburg or Berlin on the west; that the dip was 

 originally throughout to the eastward; and that the beds were desti- 

 tute of fossils and their relative age judged by superposition, accord- 

 ing to which the Stockbridge or North Adams limestone — the most 

 eastern rock in the section — would be the most recent. 



Referring to Emmons's discovery of a fossiliferous black slate at 

 Bald Mountain, New York, he stated that, according to Emmons's 

 principle adopted in 1812, this slate being to the w r est of the Taconic. 



Fig. 138.— Elkanah Billings. 



