of Edinburgh, Session 1883 - 84 . 
501 
places the bottom of the sea is covered with deposits due to 
this chemical action, principal among which is clayey matter, 
associated with which there are often concretions composed of 
manganese and iron. In other regions the reactions which result in 
the formation of argillaceous matter from volcanic products give 
rise also to the formation of zeolites. 
Among other products arising from chemical action, probably 
combined with the activity of organic matter, may be mentioned 
the formation of glauconite and phosphatic nodules, witli, in 
some rare and doubtful examples, the deposition of silica. Tlie 
decomposition of the tissues, shells, and skeletons of organisms add 
small quantities of iron, fluorine, and phosphoric acid to the in- 
organic constituents of the deep-sea deposits. 
Finally, we must mention extra-terrestrial substances in the form 
of cosmic dust. 
We now pass to the consideration of the role played by organisms 
in the formation of marine deposits. Organisms living at the sur- 
face of the ocean, along the coasts, and at the bottom of the sea, are 
continually extracting the lime, magnesia, and silica held in solution 
in sea water. The shells and skeletons of these, after the death of 
the animals and plants, accumulate at the bottom and give rise to 
calcareous and siliceous deposits. The calcareous deposits are 
made up of the remains of coccosplieres, rhabdospheres, pelagic 
and deep-sea Foraminifera, pelagic and deep-sea Molluscs, Corals, 
Alcyonarians, Polyzoa, Echinoderms, Annelids, Fish, and other 
organisms. The siliceous deposits are formed principally of frustules 
of Diatoms, skeletons of Eadiolarians, and spicules of Sponges. 
While the minute pelagic and deep-sea organisms above men- 
tioned play by far the most important part in the formation of 
deep-sea deposits, the influence of vertebrates is recognisable 
only in a very slight degree in some special regions by the presence 
of large numbers of sharks’ teeth, and the ear bones and a few other 
bones of whales. The otoliths of fish are usually present in the 
deposits, but, with the exception of two vertebrae and a scapula, no 
other bones of fish have been detected in the large amount of 
material we have examined. 
Agents . — Having passed in review the various materials which 
