J. D. Dana — Brief history of Taconic ideas. 413 



The comparison of views at the meeting resulted in inducing 

 Prof. Kogers and Prof. Hall to take the field for the study 

 of sections over the Taconic region. The season had just 

 passed when Prof Rogers made a report on his results to the 

 American Philosophical Society at Philadelphia,* sustaining 

 the views which Hitchcock, Hall, Mather and himself had be- 

 fore favored, namely : that the rocks were Lower Silurian (as 

 the term was" then used) from the Potsdam upward, but much 

 flexed and disguised by partial metamorphism. Prof. Emmons 

 mentions in his Report of 1842, on p. 147, that "Professors 

 Hitchcock and Rogers " were prominent objectors to his views. 

 We learn that Prof. Mather's views were essentially those of 

 Prof. Rogers from his New York Geological report published 

 in 1843. In his Preface he gives an interesting account of the 

 discussion. The Dr. Dana he refers to was Dr. Samuel L. 

 Dana, of Lowell, Mass. 



181$ to the close of 18 %£ / Phase I. — Such was the state of 

 opinion when Prof. Emmons's full report on the Taconic sys- 

 tem was published in 1842. 



The Taconic system of this report comprised the rocks from 

 the Hoosic Mountains westward, passing over the Hoosic Val- 

 ley, Saddle Mountain (which included Greylock), and also 

 over the high ridge of granular quartz, Oak Hill, just north, 

 the. Williamstown plain, the Taconic Mountains next west 

 on the Massachusetts boundary, and the eastern border of New 

 York west of this boundary to the Hudson. Beginning on the 

 east, the rocks were: (l)the "Stockbridge limestone," (2) the 

 " Granular quartz " and the " magnesian slate " of Greylock, 

 which are topographically north and south of one another, (3) 

 the limestone of Williamstown plain, (4) the " magnesian slate " 

 of the Taconic mountain, (5) the u sparry limestone " west of 

 the latter, and farther west, (6) the " Taconic slate." The fol- 

 lowing, commencing at the bottom, is the chronological order 

 according to Emmons, and in a parallel column, are given the 

 true equivalents (the Roman numerals giving the order of age) 

 as established by the latest investigations. 



Taconic System of 1842. Equivalents. 



6. Stockbridge limestone. II. Lower Silurian. 



5. (a. Magnesian slate of Grey- III. Hudson slate. 



! lock, perhaps a repeti- 



| tion of No. 3. 



[b. Granular quartz. I. Cambrian. 



4. Limestone. II. Lower Silurian. 



3. Magnesian slate of Taconic III. Hudson Slate. 



Mountain. 



2. Sparry limestone. II. Lower Silurian. 



1. Taconic slate. Ill, I. Hudson slate and Cambrian. 



*Proc. Amer. Phil. Soc, Jan., 1842. 



Am. Jour. Sol— Third Series, Vol. XXXVI, No. 216.— Dec, 1888. 

 26 



