TACONIG QUESTION IN GEOLOGY. 127 



the Potsdam sandstone, and in regarding as entirely distinct frona the New York system. 

 The upper limits of this Taconic system, and its relations to the members of the Cham- 

 plain division on the east side of the Champlain and Hudson valleys, vpere not at that 

 time clearly defined by Emmons. 



§ 142. In 1843 appeared the final Report by Mather uj^on the Geology of the Southern 

 District of New^ York, in which he rejected entirely the notion of the Taconic system, and 

 the whole teaching of Eaton, asserting that the Taconic was nothing more than a modified 

 form of the Champlain division of Emmons. The granular cjuartz-rock of the Taconic he 

 declared to be Potsdam ; the granular lim(^-rock, the Calciferous sand-rock with the suc- 

 ceeding Chazy and Trenton limestones ; while the overlying argillites, including the so- 

 called Hudson Eiver group, were the Utica and the Loraine shales. A similar suggestion 

 had been put forth by Messrs. H. D. and W. B. Eogers, in 1841, for the like rocks in New 

 Jersey and Pennsylvania, and was cited by Mather in support of his view. When, later, 

 in 1858, H. D. Rogers published his final Report on the Geology of Pennsylvania, the 

 Lower Taconic rocks of Massachusetts had been by Emmons traced south-westward through 

 the great Appalachian valley, in Pennsylvania, and the adjacent and subordinate Lancas- 

 ter valley. These rocks, under the names of Primal, Auroral and Matinal, were now de- 

 scribed by H. D. Rogers as local modifications of the Champlain series, — the great Auroral 

 limestone being assumed to be the representative of the Calciferous, the Chazy and the so- 

 called Birdseye and Black River subdivisions, while the Matinal slates were supposed to 

 represent the upper part of the Trenton, with the Utica and the Loraine shales. For 

 many extended details with regard to the facts in § 141 and 142, and for other points in 

 the Taconic history, the reader is referred to the author's volume on Azoic Rocks, published 

 as Report E of the Second Geological Survey of Pennsylvania, in IS'TS. 



§ 143. Coupled with this hypothesis of Mather was that of a progressive alteration of 

 these uncrystalline rocks of the Champlain division, supposed to be traced through the 

 Taconic strata into the crystalline schists of western New England, designated by Mather 

 as Metamorphic rocks ; between which and the Taconic, it was said by him : " No well- 

 marked line of distinction can be drawn, as they blend into each other by insensible 

 shades of difference." He was at length led to extend this same view to the more massive 

 gneisses and crystalline limestones of southern New York, and to conclude that these also 

 were, wholly or in great part, but altered rocks of the Champlain division, — a notion which 

 has lately found an advocate in Dana, who has also revived Mather's view of the Champlain 

 age of the Taconic quartz-rock and graniilar limestone, as will be noticed farther on. 



§ 144. In Chapters V and VI of this essay we have told the story of the Taconic 

 series as farther studied by Emmons. He soon became aware that the uncrystalline and 

 occasionally fossiliferous series of sandstones, shales, and limestones, constituting the 

 the First Graywacke, was not, as maintained by Mather, newer, but older than the Tren- 

 ton, and coupled these with the original Taconic, under the name of Upper Taconic. This 

 upper division was subsequently clearly recognized by him as a distinct and well defined 

 group, which, as early as 1846, he declared to be the stratigraphical equivalent of the Pots- 

 dam and the Calciferous of the Champlain division, while the whole Lower Taconic, 

 including not only the granular quartz-rock and the granular lime-rock, but the imme- 

 diately succeeding schists and argillites (Transition Argillite of Eaton), was assigned to an 

 horizon below the base of the Champlain division, and consequently older than the Pots- 



