on board H.M.S. 'Challenger. 3 529 



trie layers, the original nucleus being often very deeply impreg- 

 nated by spider-like ramifications of the manganese, or nearly the 

 whole pumice may be replaced by manganese. When pieces of 

 bone have formed the nucleus we have much the same state of 

 things. The compact bone of the tympanies of cetaceans does 

 not, however, appear to alter so rapidly as other bone ; and hence 

 it may be that we get ear-bones in such great numbers. 



Sharks' teeth of all sizes (one was 4 inches across the base) are fre- 

 quent, and are sometimes surrounded by concentric layers of nearly an 

 inch in thickness. A siliceous spouge {Farrea) was found imbedded in 

 two inches. 



A mass of red clay may occupy the centre of the nodule. The nucleus 

 is occasionally a mottled yellow-and-green substance, with agate bands 

 in some parts, and Glohigerina, the carbonate of lime being replaced by 

 silicate in these last. This nucleus can be cut with a knife, like new 

 cheese, or it is hard and brittle, breaking with a conchoidal fracture. 



Large flat aggregations occur which seem to have been formed on 

 hardened flat portions of the bottom. 



The Globigerina-shelh and Radiolaria are at times covered by small 

 specks of the manganese ; and in the former these are deposited in the 

 substance of the shell. 



In several soundings and dredgings to the south-west of the Canaries 

 we got very many large pieces of a branching Gorgonoid which were 

 deeply coated and impregnated with manganese, This was in a depth of 

 from 1100 to 1575 fathoms. 



In 670 fathoms, off the Desertas, the dead shells, pieces of coral, 

 Polyzoa, &c. were all coated with a thin film of the peroxide of manganese ; 

 and we have had indications of the same thing in still shallower water. 



In some of the Eadiolarian oozes, and in other deposits, we have found 

 the manganese more abundant in the upper layers than in the lower, and 

 vice versa. 



The following are the localities where we have met the manganese in 

 greatest quantities :-— 



Off the Canary Islands. 



Mid- Atlantic, between Canary and Virgin Islands. 



South-west of Australia. 



North and south of the Sandwich Islands. 



North of Tahiti. 



Generally in the South Pacific in our course between Tahiti and Val- 

 paraiso (see Map, Plate 20). 



Further observations may show that manganese abounds in those 

 places where we have much of the debris of augitic lavas. 



Abyssal Hhizopods (Bathybius). 

 The manganese nodules, sharks' teeth, &c. which we got in our 



2q2 



