NO. 14.] MINERALOGICAL COMPOSITION OF THE SAMPLES. 39 



character, so that they can be partly disintegrated by boiling, and thus cannot 

 be distinctly seen. The formation of iron concretions is not very closely 

 connected with the other chemical processes that take place in the samples, 

 and this confirms the assumption that they must owe their formation to some 

 ferruginous mineral particle or other. They are found, for instance, in great 

 quantities both in some of the samples that are of the darkest brown colour, 

 e. g. No. 14, and in some of the greyest, e. g. Nos. 6 and 7. The appearance 

 of a brown colour in the clay must also be due to a formation of 

 ferric oxide, but this has nothing to do with the process by which the 

 concretions in the clay are formed. The former consists, as already stated, 

 in a deposit on the surface of the clay, precipitated by the sea-water itself; 

 and is therefore most abundant in the most slowly formed samples, which 

 on that account are the brownest. On the other hand, the concretions in 

 the clay are certainly connected with the formation of the concretions described 

 in the "Challenger" Report, from the very deepest oceans. Here the deposition 

 of sedimentary matter takes place so slowly, that the iron and the manganese 

 of which the concretions are composed, have time to be formed in great, 

 coherent masses. 



Nor can there be said to be much connection between the formation of 

 iron concretions, and that other, not very well known, chemical process, which 

 causes the clay to acquire a firmer, more undecomposable consistency. The 

 formation of concretions will naturally bind the clay together as far as it 

 extends; but that it is very local may be seen from the fact that in a few 

 of the samples that contain most concretions of iron, such as Nos. 6 and 14, 

 the clay otherwise is very incoherent, this being the case particularly with 

 No. 6. 



2. Particles measuring 05—0 5 mm. 



In order to form an idea of the nature of the rocks that have yielded 

 material to the samples, it has been necessary to subject the sandy particles 

 in the samples, to a close examination. On a direct inspection of the sand, 

 it appeared that by far the greater part of it in all the samples, consisted of 

 quartz. To make microscopic preparations of the sand as a whole could thus 

 lead to no result, for in such preparations the other minerals would be pre- 



