Page:The Habitat of the Eurypterida.djvu/114

 have been of circumscribed area; the Buffalo pool extending from Bertie, Ontario, eastward into Erie County; the Herkimer pool being confined most of the time to the southern part of Herkimer County (See map, fig. 2). In spite of the faunules as a whole having such a restricted distribution, the Eurypterus lacustris of the Buffalo region has been found as far east as Union Springs, Cayuga County, although not at intermediate points, and E. remipes, the characteristic form of Herkimer County, has been found to the west at Waterville, town of Westmoreland, Oneida County, and still farther to the west in large numbers at Oriskany, Oneida County, at Cayuga Junction, Cayuga County, and possibly even at Buffalo. Dolichopterus macrochirus and Pterygotus cobbi are common to the two "pools."

. A careful determination and a thorough understanding of the conditions under which the Bertie waterlime was deposited are essential in the attempt to determine the habitat of the organisms found in that rock. Because no one has yet given an exhaustive treatment of all possible conditions of deposition with a final singling out of the true one; and because, moreover, the answer to this question of deposition furnishes one of the most important lines of evidence concerning the habitat of the Eurypterida, I shall take up a detailed discussion of the subject. Such a fine-grained, stratified rock might have been deposited in one of the following four ways, and these appear to cover all possibilities: (a) by chemical precipitation; (b) by bacterial precipitation; (c) by the formation of an organic accumulation of calcareous shells or plants, or both; (d) by the accumulation of clastic or fragmental material.

(a) Chemical origin: That the Bertie waterlime could not have been deposited by chemical precipitation is amply shown by its stratification and especially by its composition. A rock which is a chemical precipitate, is more likely to be massive, never showing such fine stratification as is found in the Bertie, for in the process of chemical precipitation there is no arrangement of the material by currents bringing in fresh supplies which vary slightly in color or texture and which when deposited make the separate layers which produce stratification, since in precipitation the action is more or less continuous and minute crystals are formed which either entirely make up a rock, or else cement into a compact mass, fine particles of clastic material as is the case around modern coral reefs. The texture of a chemical precipitate would be a finely crystalline one, whereas the material of the Bertie does not conform to this, for a thin section of the water