Page:The Habitat of the Eurypterida.djvu/103

 an association of finely preserved seaweeds, the eurypterids herewith described, and the following graptolites: Dicellograptus gurleyi Lapworth, Climacograptus bicornis Hall, Climacograptus bicornis var. peltifer Lapworth, Cryptograptus tricornis (Carruthers), the first three forms in great abundance. This graptolite association is one of undoubted Normanskill age. The seaweeds occur in large perfect fronds and are of the same type as those in the Schenectady shale. The eurypterids also are strikingly similar to those from the Schenectady beds" (39, 411, 412).

The eurypterid remains are very fragmentary, in fact, they are so incomplete that generic determinations are only provisional, there being but a few carapaces and fragmentary abdomina with a small number of legs and telsons rarely attached. Five genera are thought to be represented: Eurypterus, Eusarcus, Dolichopterus, Stylonurus by one species each, and Pterygotus by two species, though one of these may be a Eusarcus.

The physical characteristics of the Schenectady beds are closely similar to those of the Normanskill beds. Both consist of heavy bedded sandstones, dark in color, but highly siliceous, alternating with black shales. The sandstones are compact enough to be quarried for building and paving purposes. Both the shales, and bluestones change westward into shales, and eastward become very coarse. In the Normanskill beds pebble layers alternate with the sandstones, while in both formations mud cracks are found in the shales and subsolifluction contortions in the sandstones, structures which show a slumping motion of the sands along the shore (Berckhemer, 21). The sandstones contain eurypterid and plant remains, the latter identified as Sphenophycus latifolius, and having a remarkably thick carbonaceous test which is so high in carbon that it will burn. In the shales occur the graptolites and eurypterids, the latter not being so abundant as in the sandstones, but exhibiting better preservation.

The sediments of both the Normanskill and the Schenectady were undoubtedly derived from the east as the following facts indicate: (1) Coarse materials, conglomerates and sandstones with intercalated shales in east along Schenectady-Catskill line, passing laterally into fine black shales westward in the Mohawk Valley; (2) deposits thicker and coarser in east than in west; (3) evidences of shore conditions in sun-cracks, wave marks, and subsolifluction, in east, of conditions in quieter water farther from shore in the fine black shales westward. Appalachia was the only large land area to the east from which