OUR KNOWLEDGE OF THE BEEP SEA. 41 



engage their attention. Kircher, in his Mundns 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 ele- 

 vations the depth will gradually diminish toward the shore. I 

 say coasts with but slight elevations, for, if the shores are sur- 

 rounded 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 eight- 

 eenth century, but they were not of much value. The first at all 

 reliable were made by Sir John Ross during his well-known arc- 

 tic 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 pos- 

 sessed concerning the nature of the bottom of the sea. He admit- 

 ted 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 bot- 

 tom of the basins by the materials which seamen bring up in their 

 soundings. The dredgings almost always indicate a muddy bot- 

 tom, 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 prolon- 

 gation 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- 



VOL. XLIII.- 



