engage their attention. Kircher, in his Mundus Subterraneus, gives the ideas as to the depths of the sea that were accepted in the first half of the seventeenth century, stating that "in the same manner as the highest mountains are grouped in the center of the land, so also should the greatest depths be found in the middle of the largest oceans; near the coasts with but slight elevations the depth will gradually diminish toward the shore. I say coasts with but slight elevations, for, if the shores are surrounded by high rocks, then greater depths are found. This is proved by experience on the shores of Norway, Iceland, and the islands of Flanders."
Several soundings were taken in deep water during the eighteenth century, but they were not of much value. The first at all reliable were made by Sir John Ross during his well-known arctic expedition in 1818. He brought up six pounds of mud from 1,050 fathoms in Baffin Bay, and obtained correct soundings in 1,000 fathoms in Possession Bay, finding worms and other animals in the mud procured. Sir James Clark Ross, during his antarctic expedition from 1839 to 1843, obtained satisfactory soundings of 2,425 and 2,677 fathoms in the South Atlantic, with a hempen cord. He also dredged successfully in depths of 400 fathoms.
Meanwhile, about the middle of the eighteenth century, the first definite ideas about the formation of the bottom soil began to be advanced, although there had been speculations on the formation of alluvial layers since the time of Herodotus. In 1725 Marsilli made a few observations on the bathymetric knowledge then possessed concerning the nature of the bottom of the sea. He admitted that the basin of the sea was excavated "at the time of the creation out of the same stone which we see in the strata of the earth, with the same interstices of clay to bind them together," and pointed out that we should not judge of the nature of the bottom of the basins by the materials which seamen bring up in their soundings. The dredgings almost always indicate a muddy bottom, and very rarely a rocky one, because the latter is covered with slime, sand, and sandy, earthy, and calcareous concretions, and organic matter. These substances, he said, conceal the real bottom of the sea, and have been brought there by the action of the water. Lastly, by way of explanation, he compared the bed of the sea to the inside of an old wine cask, which seems to be made of dregs of tartar although it is really of wood.
Donati's studies on the bottom of the Adriatic Sea led him to announce, about the middle of the eighteenth century, that it is hardly different from the surface of the land, and is but a prolongation of the superposed strata in the neighboring continent, the strata themselves being in the same order. The bottom of this sea is, according to him, covered with a layer formed by crusta-
