498 Proceedings of the Royal Society 
adopted in the study. All the details of our research will be 
given in the Eeport on the Deep-Sea Deposits in the “ Challenger ’’ 
series, which will be accompanied by charts indicating the distri- 
bution, plates showing the principal types of deposits as seen by 
the microscope, and numerous analyses giving the chemical com- 
position and its relation to the mineralogical composition. The 
description of each sediment will be accompanied by an enumera- 
tion of the organisms dredged with the sample, so as to furnish all 
the biological and mineralogical information which we possess on 
deep-sea deposits, and finally, we shall endeavour to establish 
general conclusions which can only be indicated at present. 
Before entering on the subject, we believe it right to point out 
the difficulties which necessarily accompany such a research as the 
one now under consideration, difficulties which arise often in part 
from the small quantity of the substance at our disposal, but also 
from the very nature of the deposit. Since we have endeavoured 
to determine, with great exactitude, the composition of the 
deposit at any given point, we have, whenever possible, taken the 
sample collected in the sounding tube. That procured by the trawl 
or dredge, although usually much larger, is not considered so satis- 
factory on account of the washing and sorting to which the deposit 
has been subjected while being hauled through a great depth 
of water. We have, however, always examined carefully the 
contents of these instruments, although we do not think the 
material gives such a just idea of the deposit as the sample collected 
by the sounding tube. The material collected by the last named 
instrument has been taken as the basis of our investigations, although 
the small quantity often gives to it an inherent diflSculty. It was 
the small quantity of substance collected by the sounding tube in 
early expeditions which prevented the first observers from arriv- 
ing at any definite results ; but when such small samples are sup- 
plemented by occasional large hauls from the dredge or trawl, they 
become much more valuable and indicative of the nature of the 
deposit as a whole. Not only the scantiness of the material, but the 
small size of the grains, which in most instances make up deep-sea 
deposits, render the determinations difficult. In spite of the im- 
provements recently effected in the microscopical examination of 
minerals, it is impossible to apply all the optical resources of the 
