WAicoTT.] GEORGIA TERRANR 105 



that tboir equivalents may underlie the Potsdam formation of Vermont. No such 

 rocks, have, however, as yet been detected in either Vermont or Canada,. ' 



That Dr. Hunt also confounded the typical Potsdam sandstone of 

 the Adirondack^, the quartzite of the western base of the Green Moun- 

 tains, and the Primordial series described by Murray in Newfoundland 

 is shown by his statement that a few hundred feet of typical Potsdam 

 sandstone in New York are represented in Vermont, Quebec, and New- 

 foundland by thousands of feet of strata lithologically very unlike the 

 type. 2 



Jn 1867 Prof. 0. H. Hitchcock identified the Winooski marble of 

 Vermont as the Red Sandrock, and stated that Olenellus thompsoni and 

 0. vermontana occurred in the superjacent slaty layers. 3 In the same 

 volume he presents a table of the strata from the Silurian to the De- 

 vonian, inclusive, as found in Vermont, and in this connection he says 

 he considers the Taconic to be of Lower Silurian age. This included, 

 as described by Emmons, the Georgia slates. 4 



At the time of the presentation of the two foregoing papers by Prof. 

 Hitchcock a paper on the Red sandrock of Vermont and its relations 

 was rend by Mr. J. B. Perry. 5 He concluded that the Red sandrock 

 was equivalent to the Potsdam, and that the sedimentary beds below 

 the Potsdam were not Utica or Lorraine, but belong to the Primordial 

 zone of Barrande. The Potsdam is considered to be the top of the 

 Primordial, not the base of the Silurian. In the table of formations 

 the Red sandrock or Potsdam is placed at the top of the Taconic sys- 

 tem, and the Taconic slate with the quartzite limestone or conglomer- 

 ate at the base. The following year the same author 6 again stated 

 that the Red sandrock was of Potsdam age and not Medina, and he 

 subdivided the slates below into the Swan ton and Georgia series, as 

 older than the Utica slate, referring them to the Primordial of Bar- 

 rande. 



In a summary of the Geology of Vermont, by Prof. C. H. Hitchcock, 7 

 published in connection with the Geology of Northern New England, 

 it is stated, under the head of " Potsdam Group," that it includes (1) 

 black slate, or part of the " Hudson River slate" of the former report 

 of the Vermont Survey. (2) Georgia slate. (3) Red Sandrock and 

 quartz rock at the base of the Green Mountains. (4) Potsdam sand- 

 stone, the same as the original beds in New York. 



% 



•Op. cit.,p.229. 



* On the geology of eastern New England. Am. Jour. Sci., 2d ser., vol. 50, 1870, p. 85. 



8 The Winooski marble of Colchester, Vermont. Am. Assoc. Proc, vol. 16, 1867, p. 119. 



4 The Geology of Vermont. Am. Assoc. Proc, vol. 16, 1867, p. 122. 



6 Am. Assoc. Proc, vol. 16, 1867, pp. 128-134. 



6 Queries on the red sandstone of Vermont and its relations. Boston Soc. Nat. Hist., Proc, vol. 

 11,1868, pp. 341-353. 



7 The geology ol' Vermont. In Geology of northern New England, 4to, 1870, p. 2. 



