REPOET ON THE DEEP-SEA DEPOSITS. 
13 
to the spot, and the modifications, physical and chemical, which these have undergone in 
the course of time. Each of the constituent elements, whether organic or inorganic, has, 
again, its own history, and this we have endeavoured to trace by studying their nature, 
form, dimensions, and their relations to each other at the spot from which they have been 
collected by the dredge or sounding tube. For this purpose the chemical and micro- 
scopical methods recently introduced into the study of geology have been largely made 
use of. A knowledge of the various particles forming a deposit led to a rational classi- 
fication of marine deposits and to a definite nomenclature, of which we will have to 
speak further on. 
At the outset, the difficulties which surround this kind of study may be pointed out. 
In the first instance the quantity of a deposit procured in the sounding tube may be very 
small, and this, especially whenever of an incoherent nature, has undergone a kind of 
sorting in the tube itself, owing to some of the finer or coarser particles being washed out 
while being hauled up through the water. Again, the specimens preserved in spirit or 
water have undergone sorting by being shaken up during the voyage, so that the contents 
of the bottles are often arranged in layers, the heavier portions being at the bottom and 
the lighter on the top. The specimens artificially dried, when not first washed in 
distilled water, often contained crystals of sulphate of lime and other sea salts. In the 
case of samples from the dredge or trawl there had been, it was evident, much washing 
away while the apparatus was being hauled up through the water ; indeed often all the 
deposit was washed away, and only manganese nodules, teeth, bones, and rock fragments 
remained in the net. It is thus apparent that considerable care was necessary to ensure 
that, in making analyses or in choosing a sample for determining the percentage of 
carbonate of lime or other elements present, we were working with an average sample. 
As a rule we took for this purpose the specimens collected in the sounding tube and 
dried on board ship. When a difference was noted in the upper and lower layers in the 
sounding tube, these were preserved and examined separately. The results of an 
examination of the specimen from the sounding tube, frequently small in quantity, were 
compared with those obtained from an examination of a very large quantity procured in 
the trawl or dredge at the same spot, often amounting to several hundredweights. 
It is evident, then, that to make the descriptions as dear as possible, it became 
necessary to follow a systematic plan and not to deviate from it. The method finally 
adopted was chosen, after many attempts, as the best, and the one most likely to be 
followed by others in describing deposits that may be hereafter obtained from the ocean’s 
bed. This method will now be referred to in detail, and will be at once rendered intel- 
ligible by reference to the Tables in Chapter II., -where the particulars regarding each of 
the Challenger specimens are presented in synoptical form. 
In commencing the examination of a deposit, attention was first given to the 
macroscopic characters. By means of the naked eye or a hand lens, the substance was 
