til EXPEDITION OF THE " CHALLENGER " 97 



** The nature and origin of this vast deposit of clay is a ques- 

 tion of the very greatest interest ; and although I think there 

 can be no doubt that it is in the main solved, yet some matters 

 of detail are still involved in difficulty. My first impression 

 was that it might be the most minutely divided material, the 

 ultimate sediment produced by the disintegration of the land, 

 by rivers and by the action of the sea on exposed coasts, and 

 held in suspension and distributed by ocean currents, and only 

 making itself manifest in places unoccupied by the Globigerina 

 ooze. Several circumstances seemed, however, to negative this 

 mode of origin. The formation seemed too uniform : wherever 

 we met with it, it had the same character, and it only varied in 

 composition in containing less or more carbonate of lime. 



"Again, we were gradually becoming more and more con- 

 vinced that all the important elements of the Globigerina ooze 

 lived on the surface, and it seemed evident that, so long as the 

 condition on the surface remained the same, no alteration of 

 contour at the bottom could possibly prevent its accumulation ; 

 and the surface conditions in the Mid -Atlantic were very 

 uniform, a moderate current of a very equal temperature passing 

 continuously over elevations and depressions, and everywhere 

 yielding to the tow-net the ooze-forming Foraniinifera in the 

 same proportion. The Mid-Atlantic swarms with pelagic 

 Mollusca, and, in moderate depths, the shells of these are con- 

 stantly mixed with the Globigerina ooze, sometimes in number 

 sufficient to make up a considerable portion of its bulk. It is 

 clear that these shells must fall in equal numbers upon the red 

 clay, but scarcely a trace of one of them is ever brought up by 

 the dredge on the red clay area. It might be possible to explain 

 the absence of shell-secreting animals living on the bottom, on 

 the supposition that the nature of the deposit was injurious to 

 them ; but then the idea of a current suflSciently strong to 

 sweep them away is negatived by the extreme fineness of the* 

 sediment which is being laid doAvn ; the absence of surface 

 shells appears to be intelligible only on the supposition that they 

 are in some way removed, 



"We conclude, therefore, that the 'red clay' is not an addi- 

 tional substance introduced from without, and occupying certain 



193 



