524 Mr. J. Murray on Oceanic Deposits examined 



manganese. In the white varieties the sediment, after dissolving away 

 the carbonate of lime, is in some specimens abundant, in others not 

 abundant, and is either of a red or slate-blue colour. We find the 

 former colour to prevail in those soundings far from continents and large 

 islands, and the sediment is not abundant except where pumice or scoria 

 is present. The latter, or slate-blue colour, is found in those soundings 

 more or less near continents and large islands ; and it is suspected that 

 this sediment has its source chiefly from the disintegration of these 

 adjacent lands. 



Mica, quartz, pumice, scoria, and other mineral particles are met with ; 

 but in those soundings furthest from land a little piece of pumice or 

 scoria may be the only trace of mineral particles. 



In some specimens there are very many remains of organisms with 

 siliceous shells, as Eadiolaria, Diatoms, and Challengerias ; but in others 

 these remains are almost entirely wanting. In three soundings in mid- 

 Atlantic between the Canary and Virgin Islands, and in several soundings 

 in the South Pacific, manganese in the forms of grains and nodular con- 

 cretions is very abundant. As a rule, however, this substance occurs 

 rather sparingly in Globigerina-ooze. In some instances we get little 

 nodules of these bottoms, the shells as it were being run together by a 

 siliceous cement. Many small pieces of cherty-like mineral also occur, 

 which are angular and soft, and do not look as if they had been trans- 

 ported. Manganese nodules occurring in the Globigerina-ooze have 

 often a nucleus of a yellow and green colour, in which Globigerina-shelh 

 can be seen ; but their carbonate of lime has been entirely removed, and 

 replaced by a silicate. There are reasons for thinking that these indica- 

 tions of flint (?) occur only in those samples where the siliceous shells of 

 Badiolaria, Diatoms, &c. are wanting, and do not occur where these 

 organisms are present. A reexamination of all the bottoms must be 

 made before this statement can be definitely affirmed. Casts of 

 Poraminifera occur very sparingly in Globigerina-ooze ; in the purest 

 samples not at all. In those with an admixture of clayey matter we 

 have frequently one or two partial casts of a very rough character. In 

 two soundings, Nos. 211 and 301, in the Pacific, we found the Pora- 

 minifera not only filled, but also coated with a red substance, so that we 

 had both an internal and an external cast, the two being connected by 

 little rods representing the foramina of the shell. In these soundings 

 there was much clayey matter and disintegrating pumice and scoria. 



In a few soundings in the Pacific, as "No. 304, we have had a 

 Globigerina-ooze on the surface of the bottom, and a foot beneath a 

 nearly pure red or brown clay. Again, as in Nos. 268 and 307, we have 

 the reverse arrangement, a clay occupying the surface, and the deeper 

 layers having many Globigerince. In all these cases the surface-layer has 

 been normal with the other soundings in the same region as to depth. 

 In the first case we might bring in elevation to account for the 



