408 A. W. GRABAU PALEOZOIC DELTA DEPOSITS OF NORTH AMERICA 



glomerate or sandstone was found overlying these red beds, and this was 

 classed as the Upper or White Medina. Darton 8 in 1896 renamed 

 these upper white beds the Tnscarora sandstone, and the red beds beneath 

 them he called the Juniata sandstone and shale, from the Tuscarora 

 monocline and the Juniata Eiver in Pennsylvania, respectively, where 

 these formations are best shown. All the conglomerates, sandstones, and 

 shales were subsequently united by Clarke and Schuchert under the name 

 Oswego group, and as such made to represent the basal part of the Si-« 

 luric, 9 a classification widely adopted in most of the recent text-books. 



I believe I was the first to seriously question this accepted correlation, 

 and to give reasons for the belief that these conglomerates and sandstones 

 were not of the same age. This subject was for some years discussed 

 before my advanced classes at Columbia University, and was especially 

 taken into consideration during the fieldwork in the Becraft and subse- 

 quently the Schoharie regions. The subject was brought up for discus- 

 sion at the Philadelphia meeting of the Geological Society of America 

 December 31, 1904, under the title "Kelative ages of the Oneida and 

 Shawangunk conglomerates." In this communication I gave the evi- 

 dence for assigning the Oneida conglomerate to a horizon at least as high 

 as mid-Medina and the Shawangunk to the age of the Salina deposits of 

 central New York. Mr. C. A. Hartnagel, Avho had been studying the 

 Cobleskill formation of Xew York, also came to the conclusion that, since 

 the Shawangunk and associated red shales and sandstones were beneath 

 the Cobleskill, their age was to be regarded as Salina. The abstracts of 

 these communications were not published until February 10, 1906,* 

 though my own conclusions appeared in the preliminary announcement 

 for that meeting. The full paper has, however, never been published. 

 The subject was again considered in an address on the "Physical charac- 

 ters and history of some New York formations," delivered before Section 

 E of the American Association for the Advancement of Science, at Syra- 

 cuse, July 25, 1905, and published in Science of October 27 for that 

 year. 10 In that communication the age of the Oneida was shown to be 

 Upper Medina, and reasons were given to show that the Shawangunk was 

 of Salina age. In the paper these beds were also considered as possibly 

 of subaerial origin, representing delta fans formed by rivers from the 

 old Appalachian highlands. Meanwhile Mr. Hartnagel published his 

 observations in a paper entitled "Xotes on the Siluric and Ontario sec- 



8 U. S. Geological Survey Folio No. 32. 



8 Science, n. s., vol. x. No. 259, pp. 874-878, Dec. 15, 1899. 



* Bull. Geol. Soc. Am., vol. 16, p. 582. 



10 Science, n. s., vol. xxii, pp. 528-535. 



