40 Cincinnati Society of Natural History. 



which are still found, even in the most characteristic samples of the 

 red clay. 



" There seems to be no room left for doubt that the red cla}^ is essen- 

 tiall}' the insoluble residue, the ash, as it were, of the calcareous or- 

 ganisms which form the globigeriua ooze after the calcareous matter 

 has been by some means removed. An ordinarj^ mixture of calcareous 

 foraminifera with the shells of pteropods, forming a fair sample of 

 globigeriua ooze from near St. Thomas, was carefully washed, and sub- 

 jected, bj^ Mr. Buchanan, to the action of weak acid; and he found 

 that there remained, after the carbonate of lime had been removed, 

 about one per cent, of a reddish mud, consisting of silica, alumina, and 

 the red oxide of iron. This experiment has been frequently repeated 

 with different samples of globigeriua ooze, and always with the result 

 that a small proportion of a red sediment remains, which possesses all 

 the characters of the red clay. I do not for a moment contend that 

 the material of the red cla}^ exists in the form of the silicate of 

 alumina and the peroxide of iron in the shells of living foraminifera 

 and pteropods, or in the hard parts of animals of other classes. That 

 certain inorganic salts other than the salts of lime exist in all animal 

 tissues, soft and hard, in a certain proportion, is undoubted; and I 

 hazard the speculation that during the decomposition of these tissues 

 in contact with sea water and the sundry matters which it holds in 

 solution and suspension, these salts may pass into the more stable com- 

 pound of which the red clay is composed. 



" Shortly after the red clay has assumed its most characteristic 

 form, by the total removal of the calcareous shells of the foraminifera, 

 at a depth of say 3,000 fathoms, the deposit in the Pacific Ocean in many 

 cases begins gradually to alter again, by the increasing proportion of 

 the shells of Radiolarians, until, at such extreme depths as 4,575 fath- 

 oms, it has once more assumed the character of an almost purely or- 

 ganic formation — the shells of which it is chiefly composed being, 

 however, in this case siliceous, while in the former thej' were calcareous. 

 The radiolarian ooze, although consisting in great part of the tests of 

 Radiolarians, contains even in its purest condition a very considerable 

 proportion of red clay. While foraminifera are apparentl}^ confined to 

 a comparatively superficial belt, Radiolarians exist at all depths in the 

 water of the ocean. 



" The distribution over the bed of the ocean may be broadly defined 

 thus: the globigeriua ooze covers the ridges and the elevated plateaus, 

 and occupies a belt at depths down to 2,000 fathoms round the shores, 

 outside the belt of shore deposits: and the red clay covers the floor of 



