Page:The Habitat of the Eurypterida.djvu/63

 of the problem. "The Eurypterid fauna also occurs in the mud layers in the Shawangunk conglomerate, which hardly admits of any other interpretation than deposition by torrential rivers. This would make the Eurypterid fauna a fresh-water fauna, an interpretation which best corresponds with the distribution of these fossils geologically as well as geographically. The Salina series is best understood as a desert deposit. The absence of organic remains (with the exceptions noted), known to be abundant in all modern salt deposits of sea-margin origin; the thickness of the salt beds; their limitation to circumscribed basins, the red color of the lower shales, their mudcracks, all point to a continental origin" (84, 245). Clarke in reference to this fauna says: "Our present knowledge of the habits of the merostome crustaceans derived both from the living and fossil forms, indicates the shallow water or barachois origin of all sediments in which these remains abound" (36, 302). He does not, however, accept Grabau's interpretation of a torrential origin for the Shawangunk deposits, but thinks rather that they were formed in an Appalachian Gulf cut off from the ocean on the east by the Shawangunk Mountains, the material being swept down from the land and forming a delta deposit, the terrestrial waters preventing a highly saline condition in the gulf. The eurypterids, according to this view, were marine, forms caught in a gulf of not too great salinity.

In the second volume of Chamberlin and Salisbury's Geology published in 1907, the eurypterid problem is again taken up as follows: "These giants among their kind seem clearly to have been aquatic forms, but whether they were primarily marine or fresh-water habitants is not so obvious. They are wholly extinct, and their habitat can only be inferred from their associations. Some crustacean fragments that seem to belong to the same sub-class as the eurypterids (Merostomata) have been found by Walcott in Pre-Cambrian beds, but their associates are too few to throw much light on this question, though they favor a marine habitat." (Walcott considers that they favor non-marine conditions.) "A very few eurypterids appear in the Ordovician, where they are associated with marine invertebrates. In the Waterlime beds they are associated with ceratiocarids and ostracods which are usually marine, and very rarely, with certain brachiopods which are marine. In the transition beds of England, Sweden, and Russia, the eurypterids are associated more freely with marine forms, but they are also associated with the seeds of land plants and with fish which in the succeeding stage, seem to have