The Stratigraphic and Faunal Relations of the Oneonta Sandstones and 

 Shales, the Ithaca and the Portage Groups in Central New York. 



By John M. Clarke. 



This report presents a revision and summary of observations previously 

 made by the same author with reference to the position of the Oneonta sand- 

 stones, and their extent westward from the Chenango river, and adds thereto 

 more recent data bearing upon the passage of the Ithaca fauna, in the region 

 of its highest development in Cortland and western Chenango counties, 

 into the peculiar and typical fauna of the Portage group. 



It is shown that the Oneonta group, characterized by its highly colored 

 beds of shale and sandstone, and of prime economic importance on account of 

 its high-grade sandstones and flags, lies above an eastern extension of sandy 

 shales carrying the fauna of the Ithaca group. In the Chenango valley, at 

 Greene, it is overlaid, at a height of 300 feet, by a fauna having many 

 strong Chemung features, but in which certain of the Ithaca species are still 

 present. In the sections along the Genegantslet creek westward of the 

 Chenango valley, the barren red and green shales are found to alternate with 

 gray sands carrying the fossils of the Ithaca group and, in a few instances, 

 highly colored shales are observed, in which a few Ithaca species occur. 

 Over the next divide to the west, and into the valley of the Otselic river, 

 almost every trace of the red and green beds of the Oneonta group has disap- 

 peared. It is therefore concluded that the westward disappearance of the 

 Oneonta group is due to recurrent thinning of the beds, the fossiliferous 

 Ithaca beds coming in between and dovetailing with them. There is no satis- 

 factory evidence that the Oneonta beds are followed by a normal Ithaca 

 fauna, but rather by a fauna whose affinities are decidedly with that of the 

 Chemung group. The fauna of the Ithaca group is most highly developed 

 along the valley of the Otselic river and throughout Cortland county. 



In making the detailed sections of this group, the base line taken is the 



Tully limestone, and the sections result in showing outcrops of this limestone 



at points considerably south of those previously reported. This is especially 



notable along the Tioughnioga valley and in the valley of the Cheningo. In 



the Otselic valley the sections of the rocks overlying both the Tully limestone 



and the very thin layer of Genesee slate show, first, a series of barren, sandy 



shales and flagstones, which are believed to correspond with certain barren 



sands lying at the base of the Portage section at Ithaca and some points 



n 



