HISTORICAL STATEMENT 533 



shales and the lower sandstones thicken rapidly to the southwest, and in 

 Pennsylvania were also correlated with the Medina and Clinton of New 

 York. The reasons for this age determination were based on strati - 

 graphic position and lateral continuity, because there was no known 

 faunal evidence. If, however, the Pennsylvania geologists had given heed 

 to the fossils (mainly Ostracoda) that can easily be secured in the upper 

 part of the red-beds series, they would have seen nothing reminding them 

 of the Clinton, but rather of the Salinan and early Helderbergian series. 

 For more than fifty years these correlations had been fixed and the forma- 

 tions regarded as equivalents of the Medina -and Clinton. In recent years, 

 however, it has been seen that the few fossils of the red-beds series were 

 of Salinan time, and because the deposits were thought to be intimately 

 united with the Shawangunk — that is, no break in' deposition was seen 

 to separate them — both were believed to belong to the same series, and 

 hence were referred to the upper part of the Silurian system. Finally. 

 when Clarke and Euedemann found an abundance of eurypterids sug- 

 gestive of basal Salinan forms (Pittsford) in the middle of the Shawan- 

 gunk, the evidence seemed conclusive that both deposits must be regarded 

 as of late Silurian time. Accordingly, for nearly ten years we have been 

 so teaching our students in geology; but one day one of these young men. 

 Walter A. Bell, greatly surprised his teacher by pointing out that a slab 

 20 feet square in the midst of the eurypterid beds at Otisville was replete, 

 on its under side, with the burrows of ArtJtrophycus alleghaniense (see 

 plate 20, figure 2) ! This is the guide fossil for Medina time, and the 

 question was again raised, What is the age of the higher red beds? Since 

 some of these strata had yielded Salinan fossils, the further question Avas 

 to be answered, Where is the break in deposition — the disconformity — 

 between them ? 



Hartnagel 3 was the first to suggest that the High Falls red shales are 

 of Salina age, and as they rest apparently conformably on the Shawangunk 

 he further concluded that the latter represent "the invading basal mem- 

 ber of the Salina series." Grabau 4 informs us that in Ulster County, 

 New York, the Shawangunk is continuous in deposition with the red beds 

 above, "which proves the age of the red beds and the Shawangunk con- 

 glomerate to correspond to that of the New York Salina." Later 5 he 

 again refers the Shawangunk and the Green Pond conglomerates of New 

 Jersey as wellto the Salinan, and he repeats this view in 1913." Van 



3 Rept. N. Y. State Paleontologist for 1903, 1905, pp. 345-346. 



4 Science; Oct. 27, 1905, p. 533. 



5 Ibid., Feb. 26, 1909, p. 355; Sept 24, 1909, p. 415, and Jour. Geology, vol. 17, 1909, 

 p. 245. ;- ,- 



• Bull. Geol. Soc. Am., vol. 24, 1913, p. 480. 



