Page:The Habitat of the Eurypterida.djvu/11



It has been the custom to consider that all fossils are the remains of marine organisms unless obvious and indisputable evidence of their fluviatile, lacustrine, or terrestrial habitat is available; a fossil found without any other associates has been held to be marine until proved to be otherwise, but never has the suggestion been made that such a fossil was fluviatile until proved to be marine. Yet such a suggestion would be most logical, and, as we shall see, it would be far more natural than the one usually made. The early fish have always been considered normally marine, though recent studies of the character of the sediments in which their remains occur has led many of the former advocates of the marine habitat to concede that the earliest fishes lived in non-marine waters, perhaps lacustrine, but most probably fluviatile. Similarly, limestone faunas were at one time referred without question to a marine origin, but we now know that limestones of purely marine organisms may be formed by eolian deposition, as in the case of the Miliolitic limestone of the Kathiawar Peninsula of Western India (Grabau, 87, 574). There is thus no a priori reason