25G 
THE VOYAGE OF H.M.S. CHALLENGEE. 
.sulphuretted hydrogen being given off ; the latter passing into the circumambient water 
is oxidised into sulphuric acid, which in turn decomposes the carbonate of lime dissolved 
in the sea-water or existing in the form of calcareous shells, sulphate of lime being finally 
formed. The nitrogenous or albuminoid matters present in animal tissues and fluids 
break up ultimately, by a series of complex reactions, into ammonia and nitrogen ; the 
former is either liberated, or, combining with the carbonic acid, passes into solution as 
carbonate of ammonia, or becomes oxidised into nitrates. Further, the sulphur and 
})hosphorus are given off in combination with hydrogen, becoming finally oxidised into 
sulphuric and phosphoric acids, which, decomposing the alkaline and earthy carbonates 
l)resent in sea-water, give rise to sulphates and phosphates. 
]\Iurray and Irvine have shown by direct analyses that the ammoniacal salts, formed 
as indicated by the above reactions, are everywhere present in the ocean, due to the 
decomposition of albuminoid matter, ammonia being always one of the products. This 
change is accelerated by a high and retarded by a low temperature, consequently 
tropical or warm water contains much more ammonia than is found in the waters 
of temperate zones.^ The carbonate of ammonia, arising from the decomposition 
of animal products in presence of sulphate of lime in the ocean or in the bodies of 
animals, becomes converted into carbonate of lime and sulphate of ammonia. The whole 
of the lime salts in the sea may be thus available for the coral- and shell-builders.^ 
The much more rapid decomposition of the nitrogenous organic matter in the tropics 
may probably explain the greater development of coral reefs, and generally of all lime- 
secreting organisms, in tropical than in colder seas. 
The low' temperature at the bottom of the ocean and possibly also the pressure 
retard putrefaction, but it is evidently incorrect to state that putrefaction does not exist 
ill great depths,^ for everywhere there are signs to the contrary. This opinion has 
a}»parcntly been founded on some interesting but inconclusive experiments made by 
Regnard w'ith fresh w'ater,^ w'here the absence of sulphates excludes the supply of 
oxygen, w'hich in sea-water, as has been shown, is the great factor in oxidizing organic 
remains. 
From the reactions referred to above some idea may be formed of the nature and 
extent of the changes that are continually going on in the ocean, and they are referred 
to in this place in order to indicate the circumstances wdiich must be taken into con- 
.nidcration when treating of the presence or absence, the quantity, condition, and 
distribution of organic remains and other materials in deep-sea deposits. 
* Murmy and Irvine, Proc. Ihnj. Soc. Edin., vol. xvii. p. 89. 
* Murmy and Ir\’ine, lor. ril., p. 90. 
* Pelaeneer, “ Exploration de« Mere profondca,” Ound, 1890. 
* Il«-|fnnril, “ Influence dca hautea pressions sur la putrefaction,” Rev. Scientif., tom. xliii. p. 284, 1889. 
