Page:The Habitat of the Eurypterida.djvu/222

214 have lived in or along the shore of a shallow, epicontinental sea having a connection with the Atlantic or other waters to the east. In this restricted sea terrigenous deposits were formed, well represented by the Shawangunk delta. In the pools along shore, where, on account of the more sheltered conditions, only muds were accumulating, the young eurypterids lived. The larvæ were hatched in these pools and the early stages in the ontogeny were passed through, then the mature individuals sought the deeper littoral waters. Thus do Clarke and Ruedemann explain the presence of the abundant fauna composed almost entirely of young individuals in the Shawangunk shales at Otisville, New York, and, during the same period, the closely related but mature individuals in the Pittsford shales at Pittsford, New York.

A comparison, species by species of the forms from the Pittsford and Shawangunk will be given below (p. 225), and it will be seen to show that the two faunas are very closely related, indeed, almost identical except in the size of their individuals, and in the presence, in the Pittsford, of a species of Eurypterus related to a Bertie form to be considered presently. Such similarity might, if taken alone, seem to substantiate the "lagoon" theory. But it is usually impossible to draw very accurate or very far-reaching conclusions from the consideration of faunas or of deposits in a single circumscribed area or at a single horizon; one must take into account the palæogeographic conditions in neighboring regions and finally throughout the whole continent if not, indeed, the whole world, and one must consider the source of supply of sediments, the possibilities of migrations of faunas and the absolute necessity of a fauna to have a medium in which it can live from one period to another, unless we wish to revert to the belief in special creations. Thus, bearing these things in mind, we must account for the origin of the sediments of the Pittsford and Shawangunk and of the succeeding formations, the various waterlimes, which contain eurypterids. It has been demonstrated on pp. 100–6, that the conglomerates and shales of the Shawangunk and the shales of the Pittsford must have come from Appalachia, carried northwards by various rivers.

Now, assuming for the sake of argument that the succession of events during Salina time was that outlined above (p. 212) then the following conditions are implied: (1) The Pittsford and Shawangunk faunas must have constituted the ancestral stock for the Bertie fauna of Erie and Herkimer counties. (2) Throughout the long period from