98 THE CAMBRIAN. Tblll.81 



hereafter, I will now go back and give a short resume" of the history oi 

 the latter as mentioned by various authors. 



GEORGIA 6LATE8. 



The first notice we find of the slates and shales now referred to th< 

 Georgia terrane of Vermont is by Prof. Amos Eaton, iu 1818. Tin 

 argillaceous and siliceous slates and, in isolated masses, a graywack* 

 slate (Nos. 9 and 10 of his figured section) are shown to the east and wesl 

 of the Hudson River, the slates on the east alone belonging to the Oai 

 brian. 1 These slates were referred to the transition class. 2 In the nei 

 edition of his index 3 these beds are referred to the Argillite (7) and th< 

 Graywacke (9), these terms being then applied to them as seen in Rem 

 selaer County, New York, and in all of Eaton's subsequent publications. 

 It is the Argillite (1) and the First Graywacke or the Graywacke slat* 

 of the First Graywacke of the nomenclature of 1832 4 and his paper oi 

 1839. 5 On Rev. Chester Dewey's Geological Map of 1824 6 the sann 

 area in Rensselaer County is included under the term a Grey Wacke ; 

 and in part " Transition Argillite." 



In defining the limits of the Taconic System in 1844, 7 the northwarc 

 extension of Prof. Eaton's Argillite and Graywacke of Rensselaei 

 County into Washington County was called the Taconic slates, and it 

 was in this series, a mile north of Bald Mountain, that the first fossih 

 of the Olenellus or Lower Cambrian zone were found by Dr. Asa Fitcl 

 Theseslates, with their iuterbedded arenaceous layers, formed the Upp< 

 Taconic of Emuious, which he stated could be traced northward to tin 

 Canadian border. In the map accompanying Dr. Emmons's memoir oi 

 the Taconic System, published in 1844, all of the strata east of tin 

 Hudson are colored Taconic slates, or included in the Taconic systei 

 The same strata in the map of 1842, published by the Geological Sui 

 vey of New York, are included under the Hudson River group. 



Dr. Asa Fitch, a practicing physician in Washington County, Ne) 

 York, studied the local geology, and, under the headings of " Taconic 



1 Tbe Greywaoke or Grit area of the eastern part of Rensselaer County is now known to be abo"\ 

 tbe metalliferous limestone of Eaton or tbe Trenton limestone series of tbe New York State Survej 

 Tbe recent work of Mr. T. Nelson Dale, of the TJ. S. Geological Survey, establishes this and provt 

 that I was incorrect in referring this area to the Cambrian on the map accompanying the paper i 

 the Taconic System of Emmons and the use of the name Taconic in geologic nomenclature. (Ai 

 Jour. Sci., 3d ser., vol. 35, 1888, pi. 3.) It is probable that the eastern portion of the Cambrian are 

 as there mapped, to the north of the Berlin Grit area, in western Bennington and Rutland coiintu 

 Vermont, may also prove to be of Lower Silurian (Ordovician) ago. (C D. W., June, 1891.) 



2 An index to the geology of the Northern States, with a transverse section from Catskill Moi 

 tain to the Atlantic. Leicester, 1818, pp. 27-30. 



s An index to the geology of the Northern States. 2d ed., 12mo, Troy, N. Y., 1820, p. 163. 



4 Geological Text Book, 2d ed., 1832. 



e Cherty lime-rock or Corniferous lime-rock proposed as the line ot reference for State geologists ol 

 New York and Pennsylvania. Am. Jour. Sci., vol. 36, 1839, pp. 69, 70. 



6 A sketch of the geology and mineralogy of the western part of Massachusetts and a small part ot. 

 the adjoining States. Am. Jour. Sci., vol. 8, 1824, pp. 1-60. 



7 Emmons, E. The Taconic System ; based on observations in New York, Massachusetts, Vermont 

 and Rhode Island. Albany, 1844, pp. i-vii, 67, 6 plates. 



