7:50 DR JOHN MURK AY AND MR ROBERT IRVINE ON THE 



action of carbonic acid and water on the sulphide of manganese, combined with the iron 

 present, forming sulphide of iron. This reaction took place so long as there was excess 

 of ferric hydrate, and may be thus represented : — 



MnS + H ,0 + 2C0 2 = MnCO s . C0 2 + H 2 S 

 3HJ3 + Fe 2 3 = 2FeS + S+3H 2 . 



II. Sea-water, starch solution (to represent non-nitrogenous organic matter), and car- 

 bonate of manganese were placed in a vessel, and allowed to stand for several days at a 

 temperature of 80° F. (26°"67 C). It was found that sulphuretted lrydrogen was continu- 

 ously given off till all the sulphates present in the sea-water were decomposed, bicarbonate 

 of manganese (MnC0 3 .C0 2 ) being at the same time formed. It was noticed that the 

 carbonate of manganese oxidised much more rapidly in alkaline fluids than in pure water ; 

 and sea-water, it must be remembered, is probably always alkaline. 



III. Powdered deep-sea manganese nodules were placed in sea-water along with 

 decomposing mussel-flesh. In a few days the sulphates of the sea-water had been 

 reduced to sulphides ; and while the sesquioxide of iron present in the nodules was 

 thrown down as insoluble sulphide of iron, the manganese dioxide was first reduced to 

 sulphide, but finally appeared in the sea-water as soluble bicarbonate of manganese. 



These experiments show that manganese dioxide cannot exist for any time in muds 

 where there is a large quantity of decomposing organic matter, such as is nearly always 

 present in the Blue Muds of the Clyde Sea- Area and similar deposits around continental 

 lands. This result is in complete harmony with the actual observations as to the distribu- 

 tion of manganese oxides, made known by means of the dredge and trawl. What is known 

 as the Clyde Sea-Area consists of a series of submarine basins, separated from each other 

 by submarine barriers. The depth of the basins ranges from 30 to 106 fathoms, and the 

 depth of water over the intervening ridges varies from 3 to 15 fathoms. In all the 

 deeper parts of the basins there is a bluish mud, in which, as a rule, no manganese nodules 

 are found, but on the immediate surface of the deposit of Blue Mud there is a surface layer 

 with a reddish or light-grey colour, in which deposits of manganese dioxide do occur. When 

 stones are dredged from these muds many of them are, as a rule, surrounded by a dark 

 ring of manganese dioxide, marking the depth to which they have been embedded in the 

 mud. The whole upper surface of the stones has likewise a slight coating of manganese, 

 while the portion imbedded in the mud is free from these manganese deposits. 



The submarine ridges between the different lochs or basins are usually covered with 

 rocks and stones, many of which are dark coloured from a coating of manganese dioxide. 

 Very little mud is, as a rule, deposited on the shallower parts of these ridges, owing to their 

 being continually washed by tidal currents. Mud is, however, deposited among the stones 

 a few fathoms deeper on either side of these ridges, and some hollows or small depressions 

 on the barriers are filled with mud, in which small manganese nodules are frequently found 

 n great abundance. The larger stones in the positions here indicated all showed the 

 dark ring of manganese marking out the line between the mud and water. The deposits 



