10 0. B. B0GGILD. BOTTOM DEPOSITS. [norw. pol. Exp. 



No. 10 must be specially noticed, its peculiarity being that it consists of several 

 layers, of which the uppermost is of a greyish colour, while the lowest is a 

 fairly decided brown. As the ocean-bed seems very generally to consist of 

 several layers of different colours, it will be necessary to investigate this some- 

 what more fully, although the facts obtainable are not sufficiently numerous 

 to permit of a clear understanding on this point. 



The colour of each species of clay depends, as a rule, exclusively upon 

 the colour of the clayey matter itself. By washing, it will generally be 

 apparent that the finest substances composing the deposit have almost exactly 

 the same shade of colour as the entire sediment, while the sandy components 

 may have any other colour answering to their mineralogical composition, 

 although, the sandgrains are often provided with a very thin outer coating, 

 which makes their colour somewhat resemble that of the clay. This circum- 

 stance is of course particularly marked when the sand is made up mainly of 

 colourless minerals, especially quartz. If, for instance, we take a brown clay, 

 we shall see that the sand that is washed out of it, possesses a faint light- 

 brown colour, while this colour is altogether wanting in the sand that may 

 be washed out of the grey clay. It is easy to convince ourselves by chemical 

 means that this colour is due to hydrated peroxide of iron, which is deposited 

 in the form of a very thin coating round each separate grain of sand. It is 

 the same with the clay itself. Upon treating it with hydrochloric acid, the 

 brown colour completely disappears, and is replaced by the usual grey. Thus 

 here, too, this colour is produced by the precipitation of hydrated peroxide of 

 iron on the separate clay-particles. Schmelck has shown that the brown clay 

 in the bottom-samples is, on the whole, considerably richer in peroxide than 

 is the grey clay, for he has found that the proportion between peroxide and 

 protoxide varies as a rule between 1 and 2 in the grey clay, while in the 

 brown it is generally between 3 and 4. 



We may suppose this change in the proportion between the oxides of 

 iron to have occurred in two different ways. Either the transformation has 

 taken place in the clay itself by the aid of the oxygen in the sea-water, or 

 the water has deposited hydrated peroxide upon the clay by the aid of the 

 iron compounds dissolved in the water itself. In the first case the chemical 

 analysis should show that the total quantity of iron remained unchanged after 



