NO. u.J MECHANICAL COMPOSITION OF SAMPLES. 11 



the transformation ; in the second case, the amount of protoxide of iron should 

 be unaltered, while the peroxide should have increased. On looking at the 

 numerous iron analyses made by Schmelck, the first proves to be the case; 

 the average amount of iron is about the same in the brown and the grey 

 clays, when the percentage is calculated on what is left after the carbonate 

 of lime has been removed. 



There is, however, much to indicate that sea-water can deposit oxide of 

 iron upon the bottom. As I have mentioned in the report on the Ingolf 

 Expedition, it is a phenomenon of very general occurrence, that the upper 

 surface of stones lying upon the sea-bottom becomes covered with a brownish 

 coating of oxides of iron and manganese, while this is not the case, or only 

 very slightly so, with the under surface. When the stone is of such a species 

 of rock as, for instance, quartzite, which does not contain the smallest quantity 

 of iron, this coating must necessarily be deposited by the sea-water itself. 

 It is difficult, however, to imagine that a deposition such as this can take 

 place upon the stones, without also at the same time taking place upon the 

 sediment between them ; and there thus appears to be good reason to assume 

 that this fact also plays a part in the production of the brown colour of the 

 clay, although it is perhaps not of quite so much importance as the chemical 

 transformation of the constituents of the clay. 



In any case, it seems necessary to assume that the transformation of 

 the grey clay to brown can only take place in the very uppermost, exceedingly 

 thin layer, that is in immediate contact with the sea-water; for otherwise all 

 the mud upon the bottom could not but acquire the same brown colour, as 

 it is not possible to imagine the existence of differences in the sea-water itself, 

 that can cause the mud to be oxidised in one place, and not in another. The 

 only possible explanation appears to be that the grey clay is deposited so 

 much more rapidly than the brown, that the uppermost layer has not time 

 to be changed before it is covered with new sediment. We cannot, of course, 

 draw any positive conclusion from this, regarding the rapidity with which the 

 sediment is deposited, as long as we are althogether ignorant as to the length 

 of time required for the transformation; but on the other hand, this circumstance 

 is very important in estimating the relative rapidity with which the various 

 sea-bottom deposits are formed. Thus, where the conditions in the main are 

 uniform, and where there is no great variation in the composition of the 



