Page:The Eurypterida of New York Volume 1.pdf/103

 the Lower Siluric eurypterids thus far known were hence still purely marine.The investigation of this Frankfort shale fauna proves it to be restricted geographically to the exposures of the formation in the lower Mohawk valley, where it seems to pass with equal profusion through a thickness of several thousand feet. Specimens have been obtained in the Dettbarn quarry at Schenectady, the bluestone quarries at Aqueduct and Rexford Flats, on both sides of the Mohawk river; and a profuse association of Sphenothallus and the eurypterids was found in the upper part of the section described by Cumings [N. Y. State Mus. Bul. 34, p. 451] from Rotterdam Junction, west of Schenectady. In much higher beds of the Frankfort shale the same fauna was obtained in abundance at quarries at Duanesburg and Delanson, on the Schenectady branch of the Delaware & Hudson Railroad, and still farther southwest in the reentrant of the Helderberg escarpment, caused by the Schoharie creek, in exposures along that creek above Schoharie Junction. In a ravine of a small stream which joins the Cobleskill between Central Bridge and Howes Cave (mentioned by Grabau [N. Y. State Mus. Bul. 92, p. 102] on account of its fine exposure of the Brayman shale), the eurypterid fauna could be traced quite up to the Brayman shale. Thus in the western part of its range it occupies the whole thickness of the Frankfort shale, unless it is absent in the lowermost part of the formation, not yet found in good exposures in that region. The fauna does not seem to extend to the western localities, for it has not been observed in the Frankfort shale sections at Frankfort and Ilion, where the fossils have been very thoroughly studied by the junior author.

Toward the southeast the last traces of the eurypterids are found in the sandy shales exposed along the Vly, below Voorheesville. Here the eurypterid beds are

The rich faunas of the Kokomo and Salina beds (the latter containing these creatures by thousands) are all intercalated in distinctly marine deposits; the Kokomo beds carry such brachiopods as  and , and the Salina eurypterid shales Leperditias, Pterineas , cephalopods (Orthoceras, Gomphoceras), marine gastropods, Conularias, Lingulas and Orbiculoideas. The same is true of the European eurypterid horizons intercalated in the Wenlock and Ludlow beds of Great Britain, and of the Oesel beds of Russia. The latter horizon lies between the lower Oesel zone with heavy coral banks, numerous trilobites (as,  , etc.) and