Page:The Habitat of the Eurypterida.djvu/223

Pittsford to Bertie time, one or several rivers must have occupied approximately the same position, so that the Pittsford and Shawangunk faunas could escape into the estuaries when the Salina sea became too salt, and could remain there in the brackish water part of the estuary until Bertie time, when they appeared in two localities, at Buffalo, 75 miles west of Pittsford, and around Herkimer, 130 miles east of Pittsford. Taking up the first condition, we are confronted with a grave difficulty if we try to think of the Pittsford and Shawangunk fauna remaining in the Salina "lagoon" or at the mouths of estuaries flowing into that inland body of water during Vernon, Syracuse, and Camillus time, for it is evident that we must consider the Pittsford-Shawangunk eurypterids as the ancestors of those found in the Bertie, if we believe in this estuarine theory. In the succeeding pages, where I shall consider every species of eurypterid as an entity and as a member of a faunule, unless it be an isolated form, and where I shall take up the possible modes and routes of migration of species and of faunas, I shall show that the Pittsford-Shawangunk eurypterids were not the ancestors of the Bertie forms, and therefore the first condition which I mentioned at the beginning of this paragraph as a logical deduction from the "lagoon-estuary" theory is impossible, in which case it would appear that the Bertie eurypterids had no ancestors. Let us suppose, however, for the sake of argument, that the Pittsford-Shawangunk fauna did constitute the ancestral stock for the Bertie fauna and that in the dry and at times uncomfortably saline conditions of Salina time the eurypterids left their lagoon and went into the estuaries and even part way up the rivers, seeking proper salinity of water; then we should look for estuarine deposits of mud or perhaps coarser clastics in the Salina of central and western New York, and for the remains of marine organisms which are characteristic of such deposits. (For criteria of estuarine deposits see p. 77 above.) But we search in vain for estuarine, or delta, or flood-plain deposits in that region. Following upon the Pittsford are the Vernon barren red shales with their evidences of subaërial deposition with thorough oxidation (Grabau, 84, 86a, 87), and then the Syracuse salt deposits. All of this has been discussed before, and the evidence is clear that there existed no estuaries in the area under question in which the early Siluric eurypterids might have sought refuge. Thus, descendants of early Salina "lagoon" species had no place of retreat during later Salina time, and must have perished of drought, and we see that the Bertie eurypterids were doubly deprived of ancestors if they had to depend upon the Pittsford-Shawangunk fauna.