50 NEW YORK STATE MUSEUM 



"wood shales and the Shawangunk conglomerate must be regarded 

 as much later in age than formerly supposed and as has already 

 been suggested, the Shawangunk in this portion of the State 

 represents the invading basal member of the Salina. 



Recent determinations have shown that the Oneida conglom- 

 erate is no longer to be considered as the basal member of the 

 Medina, but that it belongs to the upper part of the Medina 

 series. This determination in regard to the higher stratigraphic 

 position of the Oneida demonstrates to a certain extent that the 

 Shawangunk is not to be regarded as basal Upper Siluric. 1 

 The higher stratigraphic position now assigned to the Oneida 

 makes the time interval between the Oneida and the Shawangunk 

 conglomerates less than formerly supposed when the Oneida was 

 considered as basal Medina. Seme of the reasons for con- 

 sidering the Shawangunk as of Salina age have already been 

 given. Other reasons are as follows : The Shawangunk con- 

 glomerate rests on folded and eroded " Hudson River '" strata. 

 That extensive folding and erosion had taken place previous to 

 the deposition of the Shawangunk is shown by the fact that in 

 .some places these agents have brought to view exposures of 

 rock which from the faunal contents are regarded as the Nor- 

 manskill shale of middle Trenton age. The presence of Lor- 

 raine beds shows that deposition had continued until the close of 

 the Lorraine and therefore, to allow time for the folding and 

 erosion of the strata previous to the deposition of the Shawan- 

 gunk, we must regard this conglomerate as of later age than the 

 Oneida. The almost nonfossiliferous character of the strata 

 below the Decker Ferry beds indicates that they were formed 

 during Salina time rather than during the Xiagaran period. The 

 period of the Shawangunk conglomerate was one of increasing 

 submergence 2 and on the east side of the Helderberg the suc- 

 ceeding formations progressively overlap the " Hudson River " 

 shales until finally at Becraft mountain the Manlius, the highest 

 member of the Upper Siluric rests unconformably upon the 

 *" Hudson River " shales. From these conditions of overlap as 

 shown on both the east and west sides of the Helderberg the 

 evidence is in favor of regarding the Shawangunk as Salina, since 

 the latter on the western side of the Heiderbergian barrier extends 

 much farther east than does the Xiagaran and in the same way 

 the higher formations of the L'pper Siluric are to be looked for 

 in the eastern section. 



l See Grabau N. Y. State Mus. Bui. 92. p. 126. 



2See LTrich & Schuchert. N. Y. State Pal. An. Rep't. 1901. p. 647- 



