27 



certain wherein these variations consist, as they are probably 

 dependent on the physical nature of the finest clay-particles. 

 It is rather characteristic that two of the last-named samples 

 No. 26 and 43, which have a slighter degree of coherence than 

 would be expected from their constitution , are of a distinctly 

 browner colour than the majority of the samples. This seems 

 to show that the degree of coherence of the samples has a 

 certain connection with the colour, though we are not yet able 

 to judge on what this first quality is really founded. Further 

 observations may possibly enhghten us on this point. 



With regard to these samples the colours are unusually 

 homogeneous. For the most part they are either grey or have 

 a slight brownish or reddish tinge. Only 14 of the samples 

 are designated brownish-grey, and 3 greyish-brown, one with a 

 reddish tinge, and only one sample differs from the others in 

 having a very strongly pronounced reddish-brown colour. 

 Otherwise not a single sample comes nearer to brown than 

 exactly half-way between grey and brown, and yet, in all 

 samples examined from other localities distinctly brown-coloured 

 ones have not unfrequently been found among the others. It 

 is generally difficult to tell the reason for the differences in 

 colour. They have no direct connection with the mineralogical 

 or mechanical properties of the samples, but depend partly on 

 the chemical nature of the clay ; generally the samples of the 

 most pronounced brown colour contain most sesquioxide of iron. 

 There is every reason to suppose that the clay was of a grey 

 colour when originally deposited, but that gradually by oxida- 

 tion at the bottom of the sea, it becomes browner and browner. 

 If this oxidation takes place in all the deposits, the colour 

 must be in close connection with the rapidity with which they 

 are laid down, so that the ones which are deposited most 

 slowly will have the longest lime in which to be subjected to 

 the oxidation, and will thus obtain the strongest brown colour. 

 The slowly-formed deposits will probably always be the finest, 



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