170 H. p. GUSHING PALEOZOIC IN NORTHWESTERN NEW YORK 



In their work in the Champlain valley the ^Dast season Ulricli and 

 Euedemann detected an uneonformitj' ivithin the Beekmantown at the 

 summit of Brainerd and Seely's Division A, and are disposed to argue 

 that this lower division should l^e separated from the rest of tlie forma- 

 tion and classified in the same system as the Potsdam beneath, making 

 the Lower Silurian commence with Division B of the Beekmantown. 

 With this conclusion the writer heartily agrees, and regards the argu- 

 ment as to the Beekmantown age of the Potsdam sandstone of the 

 Theresa district as sound only in so far as the correlation is made with 

 the beds of Division A which are below the break and which are regarded 

 as not properly Beekmantown at all. The Potsdam and Theresa forma- 

 tions are regarded as closely related and as to be classed in the same sys- 

 tem. How far west up the Saint Lawrence valley the true Beekmantown 

 deposits extended is not Icaown, hut it does not appear that they ever 

 reached the Theresa district. 



The correlation of the Pamelia formation is entirely due to Ulrich 

 and the evidence will be set forth by him. He regards it at present as 

 equivalent to the whole or a part of the upper division of the Stones 

 Eiver formation, as shown in the Chambersburg, Pennsylvania, quad- 

 rangle, where the entire formation has a thickness of some 800 feet, and 

 .consists of lower, middle, and upper divisions.^^ Lest this reference 

 should seem to make it equivalent to the Lowville, it should be noted 

 that Ulrich no longer regards the Lowville as of upper Stones Eiver age, 

 but puts it above that formation, his present view being that the upper 

 Stones Eiver of the Chambersburg section, Avith which he correlates the 

 Pamelia, is separated from the Lowville horizon by a thickness of 300 

 feet of limestone with an Upper Chazy fauna. ^^ The unconformity be- 

 tween the Theresa and Pamelia formations in the ISTew York section is 

 represented at Chambersburg by a 2,600 feet thickness of limestones, 

 2,000 feet of Beekmantown. and 600 feet of lower and middle Stones 

 Eiver age.^^ It should be stated also that the lower and middle divisions 

 of the Stones Eiver formation are regarded as essentially equivalent to 

 lower and middle Chazy in time, but that the comparatively small Chazy 

 basin was at this time entirely separated from the much larger sea to the 

 south and west in which the Stones Eiver deposits were laid dovni. 

 "Finally the upper Stones Eiver or Pamelia is only partially represented 



1" Letter of Novem1)er 10. 1907. 



i*Wincliell and T'lrich : Geological Survey of Minnesola. vol. iii. pt. 2. p. xc. 

 Ulrich and Scluichert : Bulletin no. 82. New York State Museum, p. 641. 



'= Letter of November It). 1907. Ulricb's more extended studies, as contained in his 

 letter of March 25, 1908, lead him to regard this break as of even greater magnitude, 

 the Theresa not representing the summit of the underlying formation. 



