500 CHEMICAL CHANGES IN THE COMPOSITION OF SEA-WATER. 



must, it may be on account of the pressure or temperature, have had the advantage over 

 the hydrosulphuric acid. 



Dr Andrussow does not make any reference to the alkalinity of the deeper waters of 

 the Black Sea. This is a point of much interest, on account of the somewhat complex 

 reactions which must take place when free carbonic acid or free hydrosulphuric acid is 

 present side by side with sulphides and carbonate of calcium. We should expect to find 

 the alkalinity very high, as in the waters drained from the Blue Muds examined by us, 

 though the excess of alkalinity would at the same time be continually reduced, owing to 

 the precipitation of carbonate of lime, as shown on page 485. 



Conclusions. — From the foregoing investigations it appears : — 



1st. That the sea-water associated with the deposits at the sea-bottom is often of 

 a different chemical composition from the normal sea-water overlying the 

 deposit, and especially so in the deposits known as Blue Muds. 



2nd. That when this water, associated with mud at the bottom of the ocean, 

 passes by circulation into the overlying water, this may be so altered that 

 the practice of inferring, from the amount of chlorine found by analysis, 

 all the other salts in sea-water, does not hold good, as has been hitherto 

 generally accepted. 



3rd. That wherever organic matter is in process of decomposition in sea-water, a 

 reduction of the sulphur salts of the alkalies and alkaline earths contained 

 therein takes place, with the result that the alkalinity of the water is 

 increased. 



±th. That when the above reaction takes place in the water at the bottom, or 

 associated with the deposit on the bottom, a portion, and sometimes all, 

 of the sulphur in the sea-water salts is removed and deposited as sulphide 

 of iron, thus giving the characteristic blue-black colour to the terrigenous 

 deposits known as Blue Muds. 



5th. That not only does this deoxidation of the sulphates and abstraction of 

 sulphur from sea-water take place in the muds, but it may in exceptional 

 circumstances take place in the sea-water itself, and then cause the 

 accumulation of hydro-sulphuric acid and sulphides in solution, as in the 

 Black Sea, there being insufficient ferruginous matter in such instances 

 to combine with the sulphur, and also a deficiency of oxygen. 



6th. That the chemical action which takes place between sea-water, decomposing 

 organic matter, and the iron of marine deposits gives important indications 

 as to the mode of formation of sulphide of iron and glauconitic matter, 

 in very many geological formations, and in some instances accounts for 

 the blue colour of many shales and other rocks. Where dead organic 

 matter, from any source, accumulates in great abundance on the sea-floor, 

 it may give rise of phosphatic rocks, oil-producing shales, and petroleum. 



' Bee Murray, " The Maltese Islands with reference to their Geological Structure, Jour. Scott. Ceog. Mag., vol. vi. p. 481. 



