32 
THE VOYAGE OF H.M.S. CHALLENGER. 
limited to deposits now forming in relatively shallow depths in more or less close 
proximity to continental land, and especially along those high and bold coasts that are 
removed to some distance from the embouchures of rivers bearing abundance of fine 
silt into the ocean. Phospluitic and glauconitic nodules appear also to be indicative of 
deep water otf continental shores. 
In typical oceanic deposits, should there be any casts of the calcareous organisms, 
these are with few exceptions imperfect or mere skeletons, and are always of a reddish 
colour from the presence of ferric oxide. Quartz particles are relatively rare, or absent, 
in deposits far removed from the continents, with the exception of those regions affected 
by floating ice. They are, however, abundant along many continental shores for many 
miles seawards. Small round wund-borne fragments of quartz and other minerals are, 
however, found in the deposits many hundreds of miles to the west of the northern 
shores of Africii and oti’ the shores of Australia. The size and nature of the mineral 
particles in an organic ooze, as well as the colour and amount of the amorphous clayey 
matter, or fine icashings of our descriptions, very frequently enable us to tell the 
position from which the specimen was collected. Volcanic fragments, and especially 
glassy fragments and pieces of pumice stone, are in many cases markedly indicative of 
a deep-sea deposit ; for instance, when these have undergone decomposition and are 
jussociated with nodules of manganese peroxide, sharks’ teeth, bones of whales and cosmic 
spherules, we arc sure that the specimen must have come from the greatest depths 
of the ocean, far removed from large masses of continental land. 
Such arc some of the main points on which we would rely for determining the position 
and dei)th from which a specimen of any deposit might have been procured were these 
unknown, but there are many others which have not been touched upon. Enough has 
been said, however, to show that at the present time a careful study of a deposit enables 
us to state with much precision the conditions under which it must have been laid down. 
The application of the same rea.soning to those geological strata which resemble 
nnxleni marine formations is at once apparent. 
