Page:The Habitat of the Eurypterida.djvu/204

196 rest of the eurypterid fauna should have been preserved. (c) If we are to consider that a single fragment of a eurypterid when found in marine strata proves that the eurypterid lived in the sea, then, provided no other proof existed to the contrary, insects, land shells, leaves, logs, spiders, scorpions and other land forms which are often floated or blown out to sea and which are found today thousands of miles from land, and have often been met with in the rocks associated with marine forms would also be considered as inhabitants of the sea. Since the reasoning given on pp. 93-193 has shown that the most significant and important occurrences of the eurypterids point to a fluviatile habitat, then the single special cases should not be cited as proof to the contrary. It is just as if we were to say that, in spite of the many abundant, well preserved floras of the order Fagales known throughout the world in continental beds from the Cretacic to the present, we were forced to conclude that birch and oak trees have always constituted part of the open marine flora, because in some dredging operations today an oak trunk and a number of birch leaves were hauled up one thousand miles from shore. Specific instances of anomalous occurrences have been cited on p. 67, but I shall give one further illustration here to show how little association may mean.

The Upper Devonic sandstones of Condroz Belgium with an aggregate thickness of 22 m., constitute the sandy phase of the Famennian shales of the lower part of the Upper Devonic. They are of interest because of the mixed marine fauna and terrestrial flora found intermingled in them; brachiopods, pelecypods, land forms including ferns, and the fish characteristic of the upper Old Red of Scotland are found associated, and the American genus Dictyospongia also occurs in this sandstone. Since at least part of the fauna is marine, and the flora is terrestrial, the eurypterids might be interpreted either as marine or fresh water forms; but inasmuch as only a few fragments have been found, the more rational interpretation would seem to be that the organisms did not live in the sea. This is further borne out by the fact that as the Upper Devonic beds are traced to the south into Germany they become pure marine limestones, in which no eurypterids have been found, but traced to the northwest they merge into the Old Red sandstone of England and Scotland which contains eurypterids and fresh water fishes. The deposits in Belgium, then, mark the meeting-place of the marine and terrestrial waters as the sea encroached from the south upon the Upper Old Red shore, and for