496 DR JOHN MURRAY AND MR ROBERT IRVINE ON THE 



some degree account for the bottom waters being more alkaline' than the surface waters, 

 as Dittmar* found to be the case from his analyses of the " Challenger" waters, as well as 

 for the variations noted in his table of the differences between the chlorine found and 

 that calculated from the destiny, t 



The " Challenger " researches have shown that there is an abundant fauna on these Blue 

 Muds, which feeds chiefly on the organic remains that fall from surface waters. If the 

 oxidation of these dead organisms were merely carried on at the expense of the oxygen 

 dissolved in sea- water immediately overlying the mud, the deeper waters might become 

 so overcharged with free carbonic acid that animal life could not exist. In such a 

 case there would be no formation of carbonates from the sulphates in the water, and no 

 formation of sulphide of iron and consequent abstraction of sulphur ; the carbonic acid 

 would simply exist in a free state. But in the changes indicated above, the sulphates are 

 being continually changed, so that in the water associated with the Blue Mud the 

 carbonates may exceed the sulphates in amount. 



Dittmar in his " Challenger " Report states the average alkalinity of 



Bottom water as 0*152 grms. C0 2 per 100 of total salts. 

 Surface water ,, 0'146 grms. ,, ,, „ 



showing a difference of 0'006. This increase of alkalinity in the deeper waters may be 



accounted for, as suggested by Murray, by the fact that the carbonate of lime shells of 



surface organisms (Foraminifera and Pteropods) are wholly or partially dissolved as they 



fall from the surface towards the bottom. There can be no doubt that this solution takes 



place in the waters through which the shells fall and also in the water at that point where 



they reach the bottom, but the above investigation seems to show that the increased 



alkalinity may to some extent be due to the interchange of water from the muds to the 



waters immediately above. It may be here remarked that when a large quantity of 



carbonic acid was found in oceanic waters it was at the bottom over Blue Muds, and 



that in some instances some of the Blue Mud was present in the bottle with the water, 



for instance at Station 169. J 



The principal reactions which occur in mud- waters may be explained by the following 



formulae : — 



(1) RS0 4 +2C = 2C0 2 + RS , 



where R is an earthy alkaline metal. § 



(2) RS + 2C0 2 +H 2 = H 2 S + RC0 3 C0 2 . 



(3) RS + RC0 3 C0 2 + H 2 = 2RC0 3 +H 2 S. 



On the hydrosulphuric acid meeting with ferric oxide (Fe 2 3 ) present in the surface layer 

 of these Blue Muds the following reaction occurs : — 



(4) Fe 2 3 + 3H 2 S = 2FeS + S + 3H 2 . 



* Dittmar, op. cit., p. 136. t Dittmar, op. cit., p. 43. % Dittmar, op. cit., pp. 126 and 129. 



§ Of course, the same reaction happens when sulphates of alkalies are reduced. 



