Page:The Habitat of the Eurypterida.djvu/241

Rh of the Bertie forms. Not only this; it actually came from the same region as the later types. For it must be apparent that the rivers of Atlantica, which furnished the deposits of the Bertie, were also in existence during Pittsford time and must have mouthed into whatever remnant there was of the Niagaran sea. It is not particularly likely that the ancestors, if so we may call them, of the Upper Siluric rivers occupied precisely the same location as the Bertie or Herkimer rivers, but undoubtedly they existed in somewhat the same general region. Therefore, what is more likely than that during Pittsford time these southward-flowing rivers from the continent of Atlantica should bring down the remains of organisms living in them? These rivers could not themselves have supplied the muds of the Pittsford shales, for they came from a limestone region, and whatever sediments they carried must have been of the nature of waterlimes. If such calcareous deposits were spread out on the flood plains of those rivers they are now no longer visible, for subsequent erosion has removed all traces of deposits of Pittsford age in Canada; but there is where a eurypterid fauna would be expected to occur, just as in Bertie time when waterlimes were deposited farther south the fine eurypterid fauna is found. This explanation makes it entirely clear why E. pittsfordensis is related to no form yet known from the Shawangunk, but has characteristics showing that it was ancestral to forms in the Bertie. New discoveries have corroborated this theory.

Professor C. J. Sarle has discovered the Pittsford fauna at a new locality in New York State. The details of this have not yet been published, but it is known that both Eurypterus pittsfordensis and Hughmilleria are common. The rock is a gray shale and the material was undoubtedly supplied by the rivers of Appalachia. Since Hughmilleria is otherwise known only from deposits derived from Appalachia it is reasonable to assume that the same rivers which carried in the muds also brought in the Hughmilleria. The abundance of E. pittsfordensis is not surprising, for if the rivers from Atlantica emptied into the Pittsford basin there is no reason why they should not bring as abundant a fauna as did those from Appalachia. If, as is to be expected, the basin in which these deposits were laid down was at times a fresh water lake, the eurypterid faunas of both river systems may have met and lived for a time in this water body. They were then killed by the sudden incursion of the Guelph sea which brought with it the remnant of the Guelph fauna found in the intercalated limestone.