Page:The Habitat of the Eurypterida.djvu/199

Rh Along an open coast exposed to the full force of the waves great boulders may indeed pile up, but they will be in a very narrow strip at the foot of the cliffs and will rapidly decrease in size until within but a few feet from shore no large ones will be found and those which do occur will be in only a thin layer wedging out seaward. Moreover, a boulder conglomerate formed along a seacoast would almost certainly be fossiliferous, as I shall point out below. Such a conglomerate might, however, easily be piled up by the waters of the swift and powerful torrents which periodically occur in desert regions. In large basins of inland drainage the rivers flowing down the enclosing mountains bring in great quantities of debris which is coarse and bouldery near the mountains and finer further out. Davis records that "A great part of Persia consists of large basins enclosed by mountains and without outlet to the sea. Long waste slopes stretch forward five or ten miles with a descent of 1000 to 2000 feet, stony near the mountain flanks and gradually becoming finer textured and more nearly level. The central depressions are absolute deserts of drifting sands with occasional saline lakes or marshes" (87, quoted from Davis, 50, 588).

(b) Faunal. Throughout the Old Red sandstone of Great Britain and the continent, typical marine organisms are absent except where this facies interfingers with the Devonic marine facies. The types of life represented in this whole series are few and yet of exceeding interest, since they are among the earliest of land forms, such as scorpions, insects, freshwater crustacea, fish and eurypterids, while the flora, though much poorer than that from the Gaspé sandstone of New Brunswick, yet shows the presence of ferns, coniferous trees and vascular cryptogams. The Caledonian Old Red, which is largely conglomeratic, has yielded comparatively few fossil remains, but in the Pterygotus-or Carmylie- sandstones of Forfar, Pterygotus anglicus has been found associated with Parka decipiens and at a higher horizon Cephalaspis and Pteraspis occur, and still higher the Acanthodian beds of Turin with a good fish fauna as well as Pterygotus anglicus and Stylonurus ensiformis. Thus, in the Caledonian Old Red, a series 12,500 feet or more in thickness, the fish and eurypterids are the only abundant organisms. This single faunal fact would be sufficient, even though all other types of evidence were wanting, to make me say that those two groups of organisms lived in the rivers (see criteria, p. 77 above). In the Orcadian the fauna is more