III. 



MINERALOGICAL COMPOSITION OF THE SAMPLES. 



After treating of the mechanical nature of the samples, and the results 

 that could be obtained by washing, it still remains to look at the samples from 

 the other side, and examine their composition from a mineralogical point of 

 view. One circumstance belonging to this side of the question has already 

 been discussed in the preceeding section, namely the amount of clayey matter 

 in the various sizes of grains; for this plays a very important part in the 

 composition of the samples, which cannot be lost sight of in treating of this 

 composition. In the following pages, the relation between the remaining minerals 

 will be as far as possible determined. 



For practical reasons, the treatment of each size of grains has been taken 

 separately, so that the particles of more than 0"5 mm. are examined directly 

 with a lens, while the particles between 0'05 and 05 mm. are axamined as 

 microscopic preparations. The still finer particles are not considered here, as 

 the separate minerals in them cannot be accurately distinguished from one 

 another, and the proportion between them may be assumed to correspond fairly 

 well with the proportions of the coarser particles. The particles of more than 

 0'5 mm. on the other hand, may sometimes give valuable information 

 especially regarding the mineral combinations, or rocks present, which 

 cannot be obtained from the finer particles. In this particular, however, the 

 bottom-samples of this expedition are rather unsatisfactory, as few of them 

 contain these coarser particles, which, moreover, in no case attain a greater 

 size than 2"5 mm. Thus one of the most important means of determining the 

 species of rock that have furnished the material of the samples is wanting here. 



