MANGANIFRROUS NODULES IN BOULDER-CLAY. I39 



with a large quantity of sand." It is possible that the two 

 materials have a similar source; both are found only in soils 

 overlying clay and which contain chalk. Probably an abun- 

 dance of chalk is necessary for the formation of the nodules, as 

 it is well known that whereas in the presence of acids manganese 

 exists in its stable compounds in the manga.nous state, in the 

 presence of alkali it becomes oxidised and forms the ma.nga.nic 

 compounds. Therefore in an alkali or chalky soil alone could 

 nodules or cement, in which manganese exists as the peroxide, be 

 formed. Manganese peroxide is usually found, as in these cases, 

 associated with ferric oxide and the lower oxide of manganese. 



The following may be the explanation of the occurrence of 

 these nodules : — Surface soil contains the silicates of iron and 

 manganese, but these are decomposed by the soil acids, and 

 salts of iron and manganese are formed in solution. In the presence 

 of an alkali these salts decompose and precipitate the oxides 

 of the metals. At the same time the manganese being in the 

 condition of a free oxide would become more fully oxidised by 

 the action of the air in the soil. To prove the truth of this 

 supposition a solution of manganese sulphate was taken and on 

 the addition of ammonia or other alkali, oxidation at once took 

 place in the presence of air, the white precipitate first formed 

 becoming brown, and in the course of 24 hours almost black. 

 This precipitate on examination was found to consist partially of 

 the higher oxide of manganese liberating chlorine from hydro- 

 chloric acid. The slightest acidity, even that caused by excess 

 0/ carbonic acid in the solution, was sufficient to prevent this 

 oxidation even when so powerful an oxidiser as hydrogen per- 

 oxide was employed. This precipitation may resemble crystal- 

 lization, in taking place from a particular point, and the sand 

 adhering to the growing particle would become cemented up into 

 the nodule. 



[At the reading of the paper, iMr. T. S. Dymond, F.I.C., 

 F.C.S., made some remarks, which are printed as follows in the 

 form of a Note : — 



Manganiferous nodules are not infrequently met with on the bed of the 

 deep sea. They have been found near the Canaries, to the south west of 

 Australia, in the Northern Pacific Ocean and elsewhere. These nodules are 

 said to have the appearance of urinary calculi, are brown in colour and have 

 a structure shewing superposed layers of clay. Analysis shews that they 

 consist chiefly of the oxides of iron and manganese, the latter peroxidized, 



