Page:The Habitat of the Eurypterida.djvu/80

 their distribution, origin and their included organic remains. In regard to the origin he says: "The rivers which discharge into the Severn estuary, draining, as they do, a catchment basin of 9193 square miles, are the chief sources of supply" (264, 611). A source of secondary, but by no means slight importance is the sea, which has worn off material from the cliffs and which has carried muds into the Severn. As Sollas has fully explained, though the details cannot here be given, a small part of the silt which is brought down by the rivers may be deposited in the estuaries themselves, but the greater portion is carried seaward, "so that the final resting-place of the sediment of the Severn is situated some distance out to sea." A microscopic examination of the muds from a large number of localities on both sides of the Severn and along its tributaries revealed the following organic remains: "Coccoliths and rarely coccospheres, both of the ordinary cyatholith type so common in adjacent seas and in the Atlantic ooze; Foraminifera such as Miliola, Textularia, Nonionina crassula, Polystomella umbilicata, Rotalia sp., Spirillina sp. . . . spicules of Alcyonaria rarely; fragments of Echinoderm skeletons and minute spines: and triradiate spicules of Calcisponges, probably derived from Sycandra ciliata and S. compressa. The siliceous constituents are chiefly sponge-spicules, very rarely Radiolaria, and a variable quantity of Diatoms." The remarkable feature about these remains is that they are all marine, and yet they sometimes occur on the banks of the rivers at a great distance from truly marine waters. Moreover, the remains which are found are of organisms not living within many miles of the places where they occur, for Sollas has carried out a careful investigation of the fauna along the coast. He says: "Sponges do not grow anywhere so near Bristol on this side of the Channel as Portishead and Weston; Lynton, which is about 60 miles away, is the nearest possible locality; while Ilfracombe, about 15 miles further west, is well known as a rich collecting ground for both siliceous and calcareous sponges, and a host of other marine forms, including sea urchins and starfish, which might well furnish the echinoderm network and spines so frequent in the ooze. On the other side of the channel one would need to go to Bridgend before meeting with much in the way of shore life, and I doubt, after a hasty visit to that locality, whether much would be found there; a good deal farther west is Tenby, and no naturalist needs to be informed of the luxuriant growth of all kinds of marine animals, including sponges to be met with there" (264, 619). Sollas clearly shows that the