1875.] Cruise of H.M.S. ' Challenger: 39 



the Atlantic, an indraught from the Southern Sea. The more the question 

 is investigated the less evidence there seems to me to be of any general 

 ocean circulation depending upon differences of specific gravity. It seems 

 certain that, both in the Atlantic and in the Pacific, the bottom-water is 

 constantly moving northwards ; and I am now very much inclined to refer 

 this movement to an excess of precipitation over the water-hemisphere, 

 a portion of the vapour formed in the northern hemisphere being carried 

 southwards and precipitated in the vast southern area of low barometric 

 pressure. I hope to enter fully into the discussion of this matter on a 

 future occasion. The temperature of the water is greatly lower in the Pacific 

 for the first thousand fathoms than in the Atlantic in the corresponding 

 latitude of 35° N. There is one very remarkable difference between the 

 two basins : while in the Atlantic it seems certain that the temperature 

 sinks gradually, though very slightly, for the last thousand fathoms to 

 the bottom, it appears that in the Pacific the minimum temperature of 

 1 0, 7 C. is reached at a depth not greater than 1400 fathoms, and that from 

 that depth to the bottom the temperature is the same. 



The soundings from Yokohama to Honolulu are remarkably uniform 

 in depth, the twenty-two soundings on one line, which are unaffected by 

 the neighbourhood of land, giving an average of 2858 fathoms. The 

 nature of the bottom is also very uniform ; and, according to the nomen- 

 clature which we have adopted, it is, in each case, noted on the chart as 

 " red clay." It is usually, however, somewhat greyer in colour than the 

 typical " red clay," and contains a large proportion of the tests of sili- 

 ceous organisms (a proportion which increases with increasing depth), and 

 a considerable quantity of pumice in different states of comminution 

 and decomposition. The clay contains scarcely a trace of carbonate of 

 lime, although the surface swarms with ooze-forming foraminifera. In 

 some cases the trawl came up half full of large lumps of pumice, which 

 seemed to have been drifted about till they were water-logged, and to be 

 softening and becoming decomposed ; these pieces of decomposing pumice 

 were often coated and pervaded throughout with oxide of manganese. 

 Over the whole area the red clay was full of concretions, consisting 

 mainly of peroxide of manganese, round, oval, or mammillated and very 

 irregular, varying in size from a grain of mustard-seed to a large potato. 

 "When these concretions are broken up, they are found to consist of con- 

 centric layers having a radiating fibrous arrangement, and usually starting 

 from a nucleus consisting of some foreign body, such as a piece of pumice, 

 a shark's tooth, or a fragment of any organism — as, for instance, in one 

 case a piece of a Hexactinnelid sponge of the genus Aphrocallistes, which 

 was preserved as a very beautiful fossil in the centre. The concretions 

 appear to form loose among the soft clay ; the singular point is the amount 

 of this manganese formation, and the vast area which it covers. 



We were particularly successful, during this cruise, in getting good 

 samples of the fauna from great depths ; and we found that the fauna of 



