REPORT ON THE DEEP-SEA DEPOSITS. 
255 
from the decomposition of their waste products and dead bodies, — cannot but work 
continual and extensive changes in the internal constitution of the sea-water salts and of 
the materials in suspension in sea- water or lying on the floor of the ocean, the intensity 
of these changes varying with the temperature, the amount of sunlight, and other 
conditions. 
Carbon, hydrogen, oxygen, nitrogen, sulphur, and phosphorus may fairly be regarded 
as entering into the composition of the tissues and fluids of all marine organisms ; in 
addition, carbonate of lime, silica, and other substances entering into the composition of 
the hard parts may be regarded as essential to the life of numerous species of animals 
and plants.^ When marine organisms cease to live the resolution of their complex com- 
pounds at once begins. The carbon and hydrogen pass off mainly as carbonic acid 
and water, the nitrogen forms ammonia, and the sulphur and phosphorus give rise to 
volatile sulphuretted and phosphuretted compounds ; in short, decay takes place accom- 
panied by all its well-known phenomena.^ The skeletal structures of the organisms 
become altered at the same time, and, passing into solution, may ultimately be wholly 
reduced, in the presence of sea-water, into their ultimate inorganic components. At 
the bottom in great depths the process of decay might be an exceedingly slow one 
were the only available oxygen that which is present in solution in the sea. There 
is evidence, however, of some remarkable chemical reactions which it is desirable here 
to indicate. 
The analyses of sea-water inform us that earthy and alkaline sulphates make up a 
very large part of the total sea- water salts. When these are exposed to the action 
of carbon, or of organic matter, which, of course, contains carbon, the sulphates are 
reduced and sulphides formed ; the carbon unites with the oxygen, formerly combined 
with the metal and metalloid, to form carbonic acid.® Thus for every molecule of 
sulphate decomposed in this way one molecule of sulphide and two molecules of carbonic 
acid are formed. As, practically, all the carbon of marine organisms must thus ulti- 
mately be resolved into carbonic acid, the quantity of that acid produced in this 
way must be enormous, and cannot but exert a great solvent action not only on the 
dead calcareous structures, but also on the minerals in the muds on the floor of the 
ocean. Were these reactions to end at this stage the bottom of the sea would soon 
become so poisoned by sulphides as to be unfit to support either animal or vegetable 
life. As soon, however, as the sulphides are produced, the carbonic acid, which is formed 
at the same time, decomposes the sulphides, forming earthy and alkaline carbonates, 
1 Pouehet and Chabry, “ De la production des larves monstrueuses d’Oursin, par privation de cbaux,” Gomptes 
Bendus, tom. cviii. pp. 196-198, 1889; “ L’eau de mer artificielle comme agent t4ratogenique,” JoMrnnZ de VAnatomie, 
1889, pp, 298-307. 
^ These changes are not, of course, due to simple oxidation, hut are brought about in a large measure by the influ- 
ence of organisms familiarly named Bacteria, it being now generally accepted as a fact that all putrefactive changes are 
brought about or initiated by these minute organisms. 
3 Murray and Irvine, Proc- Roy. Soc. Edin., voL xvii. p. 93. 
