404 THE CAMBRIAN. [bull. 81. 



horizontal strata of that State, relying on the evidence of fossil remains, had brought 

 out results in the main quite consistent with the determinations of the Virginia and 

 Pennsylvania strata. 



Iii an address before the Association of American Geologists and Nat- 

 uralists, Prof. Henry D. Kogers, in speaking of the tracks in the sand- 

 stone of the Connecticut Valley, says : 



Of the organic remains, through an investigation of which alone we can hope to 

 establish the position of these strata in the scale of time, or reach definite conclusions 

 respecting the physical conditions under which they were produced, the most instruc- 

 tive are the remarkable bird* tracks, brought to light by Prof. Hitchcock, in Con- 

 necticut and Massachusetts. 



Guided by mere lithological resemblance, Maclure imagined this stratum to be the 

 equivalent of the Old Red Sandstone of England. 1 



These passages imply that Prof. Henry D. Eogers considered pale- 

 ontological evidence of the highest value in correlation, although in his 

 work in Virginia he relied largely upon stratigraphic relations and lithol- 

 ogy for the correlation of the Virginia with the Pennsylvania formations. 



The correlation of the sandstone beneath the Trenton and Maguesian 

 limestones of Pennsylvania, by Prof. H. D. Eogers and those that suc- 

 ceeded him, was based upon the stratigraphic position of the sandstone 

 and the presence of Scolithus linearis, a fossil believed to be common to 

 the Potsdam sandstone of New York and the lower sandstone of Penn- 

 sylvania. 



The evidence of the identity of the sandstone with that of the Pots- 

 dam sandstone of New York, on the stratigraphic succession and posi- 

 tion, is as follows: 



(1) The formation is beneath a series of limestones, a portion of which 

 is identified with the Trenton limestone by the contained fossils. 



(2) The sandstone rests uncon form ably upon the crystalline gneisses 

 forming the basal rocks of the Paleozoic period of Pennsylvania. 



(3) The lithologic characters of the sandstone formation corresponded 

 to that of the Potsdam sandstone of New York. 



The paleontologic evidence is the presence of the annelid borings 

 called Scolithus linearis in the sandstone of New York and Pennsyl- 

 vania. 



When once established this correlation was adopted and used by the 

 first survey of Pennsylvania and also the second, but not altogether 

 without protest by some of the workers in the latter. Mr. d'Invilliers* 

 calls attention to this correlation of the Potsdam in the following words: 



It would be safer to name this formation the Beading sandstone, but in the descrip- 

 tions of its outcrops along the Little Lehigh, the Lehigh, and the Delaware Rivers, 

 in Vol. I of this report, it has been called Potsdam sandstone, taking for granted that 

 any sand formation underneath the Maguesian limestones of the Great Valley must 

 be the same sand formation which in northern New York underlies the Corniferous 

 [Calciferous?], Chazy, and other limestones of the Mohawk Valley. 



1 On American geology and present condition of geological research in the United States. Am. 

 Jour. Sot, vol. 47, 1844, p. 248. 



a The geolotry of the South Mountain Belt of Berks County. Second Geol. Surv. of Penn., D3, vol, 

 2, 1883, p. 99. 



