Page:The Habitat of the Eurypterida.djvu/62

 to the land. Chamberlin says further that the eurypterids are found in abundance in fresh-water deposits with only a few trails of annelids suggesting marine conditions; they are assumed, therefore, to have been marine first and then fresh water, but in this case also why may we not consider that these forms were carried out to sea, rather than that they lived in marine water?

In direct opposition to this line of argument, Zittel in his Grundzüge der Palæontologie (327, 527) offers the following: "The Eurypterida are found associated with Graptolites, Cephalopods, and Trilobites in the Ordovician of Bohemia and North America; with marine Crustacea (Phyllocarids and Ostracods) in the Silurian; with Ostracoderms and Arthrodires in the Devonian; and with land plants, scorpions, insects, fishes, and fresh-water amphibians in the productive Coal Measures. It is apparent, therefore, that from being originally marine forms, they became gradually adapted to brackish, and possibly even to fresh water conditions."

Clifton J. Sarle in 1898 discovered a new eurypterid fauna at the base of the Salina, Middle Siluric, of western New York (240). This formation had hitherto been considered particularly barren of fossils, but Sarle found in two layers of the Pittsford black shales such an abundance of eurypterids that some layers were "literally packed" with their remains. The two shale beds are intercalated between dolomite layers which, Sarle remarks, represented more open water and were apparently unfavorable to the eurypterids. The occupation of the black shales by these animals "was apparently of comparatively short duration, merely an incursion, as it were, since the black shale all told does not exceed 2 feet in thickness. The fact that the eurypterids are often dismembered and their parts distributed over considerable areas, and that a dozen or more are frequently found side by side . . . . suggests that they may have been drifted up by a current. On the other hand, the fine preservation of much of the material, extending even to the delicate appendages, shows that the currents were very weak, thus practically leaving the animals in the position of death or molting" (240, 1086).

A. W. Grabau in his Physical and Faunal Evolution of North America during Ordovicic, Siluric, and Early Devonic Time (1909) makes the facts of distribution an argument in favor of a fluviatile habitat, thus calling attention to one of the most important aspects