done on board H.M.S. ( Challenger. 3 607 



came up on the 17th June. It is an irregular nodule, about 1| inch 

 long, of a brownish-black colour, having its outside surface uiamuiillated 

 all over. This mammillated surface is so peculiar that, by its means, the 

 manganese may be at once recognized. When broken it is found to 

 consist of irregularly concentric layers of peroxide of manganese, alter- 

 nating with fine seams of calcareous and earthy matter. It contains a 

 small, white, earthy nucleus. The broken surface resembles the figuring 

 of polished walnut wood. It consists of peroxide of manganese, alumina, 

 iron, silica, small quantity of lime, magnesia, cobalt, and phosphoric acid. 

 Heated in the tube it gives out, like all these concretions, water with a 

 strong alkaline reaction. 



The most remarkable occurrence of peroxide of manganese on the 

 bottom was met with on the 18th February, in latitude 35° 45' N. and 

 longitude 20° 12' W. The dredge was put over in 1500 fathoms, and 

 came up full of dead coral of a jet-black colour on the surface. Some 

 of the sticks adhered to large black masses, and on breaking them the 

 inside was seen to be perfectly white, the black substance forming merely 

 a very thin rind which cracked off easily on receiving a smart blow. 

 This black rind, as well as the masses to which some of the sticks were 

 attached, consisted of peroxide of manganese, the white part or inside 

 having the composition of ordinary coral (chiefly carbonate of lime). The 

 black masses to which some of the sticks were attached present, like the 

 concretions already described, a minutely mammillated appearance on the 

 outside, and when broken across are seen to consist of concentric layers, 

 blacker and more compact towards the outside, and browner and more 

 earthy towards the inside. The layers are separated from each other by 

 numerous very fine layers of mud, chiefly carbonate of lime. They 

 increase in number towards the inside, and in some instances can be 

 seen to be composed in part of fragments of foraminiferous shells. The 

 black mass was found on analysis to consist of peroxide of manganese, 

 alumina, oxide of iron, silica, small quantities of lime and magnesia, and 

 traces of copper, cobalt, and phosphate of lime. Compared with the 

 manganese concretions already described, they appear to have the same 

 chemical composition, and their internal structure in layers points to a 

 similar mechanical origin ; in fact they differ from the others only in 

 being fragments of much larger concretions. Where the coral sticks 

 adhere, they do not penetrate into the mass at all, but their flat roots 

 are as sharply divided from the black mass as the black rind is from the 

 inside coral. 



On the 27th June, amongst the concretions, a fragment of slate, coated 

 on the outside with mammillated peroxide of manganese, was brought up. 



The preceding notes on the occurrence of the manganese nodules was 

 written at the Cape of Good Hope, and sums up our knowledge of the 

 subject at the close of the Atlantic cruise. In the Antarctic Ocean the 

 soundings obtained showed in a remarkable manner the general com- 



VOL. XXIT. 2 X 



