22 NATURAL SCIENCE. march. 



believed by the authors to be due mainly to the decomposition of 

 volcanic products. They do not deny, however, that a small quantity 

 may be derived from the land. 



Concretions rich in hydrated oxide of manganese were found in 

 the Atlantic, Indian, and Pacific Oceans. They were frequently 

 brought up by the trawl from great depths in extraordinary numbers. 

 Thus, from one haul in the South Pacific between two and three 

 bushels were obtained, together with 50 bones of whales, 1,500 

 sharks' teeth, 6 ice-borne pebbles, and 12 rounded pieces of pumice. 

 The concretions vary in size from microscopic particles to large 

 masses, of unknown dimensions, from which fragments have been torn 

 off by the action of the dredge. The common form is that of more or 

 less rounded or nodular masses, varying from i to 15 cm. in diameter. 

 The larger nodules frequently contain several nuclei. The deposi- 

 tions commenced round several foreign bodies lying near each other 

 on the bed of the sea, and increased so as finally to enclose them all 

 in one compound nodule. The nuclei are of the most varied charac- 

 ter. They consist of fragments of pumice, lapilli, sharks' teeth, ear- 

 bones, sponges, and even portions of the local deposit. A concentric 

 arrangement is seen in section. This is brought out by a variation 

 in colour in the successive zones, the lighter zones containing a 

 larger admixture of clayey or earthy material. The manganese 

 hydrate is opaque in the thin sections, and without crystalline form. 

 The characteristic dendritic structure may, however, be seen in the 

 lighter-coloured layers of the nodules. 



Dittmar's experiments indicate that the oxygen present is more 

 than sufficient to form a binoxide of manganese. Renard concludes 

 from his analysis that the condition of the manganese as regards 

 oxidation and hydration, is expressed by the formula MnO^-f i H,0, 

 and that this compound is associated with 26-7 per cent, of limonite. It 

 must not be supposed that the nodules are pure manganese com- 

 pounds. They always contain hydrated ferric oxide, as well as 

 clay and other constituents. Dr. Gibson subjected a very large 

 quantity of the material of the nodules to an exhaustive examination 

 for the purpose of determining the presence or absence of the rarer 

 elements. In addition to the ordinary constituents, he found 

 tellurium, lead, copper, molybdenum, thallium, vanadium, zinc, 

 nickel, and cobalt. Nickel is present in sufficient abundance to 

 be estimated, even in small quantities of material. 



Mr. Murray believes that the manganese has been chiefly derived 

 from the decomposition of the basic volcanic material with which the 

 nodules are so frequently associated. The amount of manganese 

 present in this material is, however, so small, that if the nodules 

 obtained their supply from this source they would probably be 

 embedded in such a mass of clay as not to be obtainable in great 

 numbers by the dredge. We accordingly agree with the opinion 

 expressed by M. Renard, in a footnote, that the bulk of the 



