352 Wyville Thomson— General Ocean Circulation. 
are derived mainly from the disintegration of shore rocks, and 
familiar, of every age. In water of medium depths down to 
about 2,000 fathoms, we have in most seas a depoais of the 
now well-known globigerina-ooze, formed almost entirely of the 
shells of foraminifera living on the sea-surface, and which after 
death have sunk to the bottom. This formation, which occu- 
pies a large part of the bed of the Atlantic and a considerable 
part of that of the Pacific and Southern Seas, is very like chalk 
in most respects, although we are now satisfied that it is being 
laid down as a rule in deeper water than the chalk of the Creta- 
ceous period. 
Tn depths beyond 2,500 or 3,000 fathoms no such accumula- 
tions are taking place. The shores of continents are usually 
too distant to supply land detritus, and although the chalk- 
building foraminifera are as abundant on the surface as they 
elsewhere, not a shell reaches the bottom; the carbonate of 
lime is entirely dissolved by the carbonic acid contained in the 
water during the long descent of the shells from the surface. 
It therefore becomes a matter of very great interest to deter- 
mine what processes are going on, and what kind of formations 
are being laid down in these abyssal regions, which must at 
present occupy an area of not less than ten millions of square 
es. 
The tube of the sounding instrument comes up from such 
abysses filled with an extremely fine reddish clay, in great part 
amorphous, but containing, when examined under the micro- 
scope, a quantity of distinetly recognizable particles, organic and 
inorganic. The organic particles are chiefly siliceous, and for 
the most part the shells or spines of radiolarians which are 
living abundantly on the surface of the sea, and apparently 10 
re or less abundance at all depths. The inorganic particles 
are minute flakes of disintegrated pumice, and small crystalline 
gments of volcanic minerals; the amorphous residue is prob- 
ably principally due to the decomposition of volcanic products, 
and partly to the ultimate inorganic residue of decompose 
organisms. There is ample evidence that this abyssal deposit 
is taking place with extreme slowness. Over its whole area, 
and more particularly in the deep water of the Pacific, the 
dredge or trawl brings up in large numbers nodules very itreg- « 
ular in shape, consisting chiefly of sesquioxide of iron and per- 
oxide of manganese, deposited in concentric layers in a matrix 
of clay, round a nucleus formed of a shark’s tooth, or a piece of 
