40 0. B. B0GGILD. BOTTOM DEPOSITS. [norw. pol. exp. 



sent in only very small quantities, so that the differences that possibly existed 

 between the several samples, could not be clearly brought out. It was there- 

 fore necessary to separate the quartz from the other minerals, and for this 

 purpose acetylene bromide mixed with ether until the specific gravity was 

 2*85, was used. By this means the quartz and the felspar on the one side 

 were separated from the great majority of minerals on the other. In the 

 case of the particles that consist of a single mineral, the separation can be 

 made very complete; but there are of course always a certain number of par- 

 ticles that consist of a very fine-grained mixture of several different minerals. 

 There is no definite specific gravity for these, and they may therefore enter 

 both sections. The same may be said of the iron concretions, which may 

 have a very different specific gravity, according to their greater or slighter 

 impregnation with ferric oxide. On the other hand, all the conglomerated 

 clay that is found between the grains of sand, will come among the 

 lighter constituents. The percentage of the two parts of sand was directly 

 determined by weighing. As there was only a very small quantity of sand 

 in some of the samples, it was impossible in their case to make any separa- 

 tion; and as an examination in any other way can give no result where it 

 is a question of pointing out such small differences as those under discussion, 

 the examination of these samples has been altogether omitted. 



a. The Heavier Particles. The mode of treatment here was to count 

 100 grains of each sample on a slide, and the percentage of the several mi- 

 nerals is then directly given. The percentage in numbers must correspond 

 fairly accurately with the percentage in weight. It is true that certain of the 

 minerals, especially magnetite, have a considerably higher specific gravity 

 than the others; but in a like degree the size of the particles will be less. 

 The sizes of grains that were indicated as obtained by washing, are only 

 applicable accurately to rounded quartz-grains; considerably smaller grains of 

 the heavier minerals will continually be washed out among them. 



The table below gives first the percentage of minerals with a higher 

 specific gravity than 2 - 85, and next, the proportion among these of the 

 various minerals. A cross under any of them indicates that it is not found 

 among the 100 minerals counted, but on searching in the remainder of the 

 preparation. It is thus highly probable that such a mineral is present in a 

 percentage of less than 1. 



