REPORT ON THE DEEP-SEA DEPOSITS. 
195 
in Deep-Sea Deposits, though they are much more abundant in some of the red clay 
regions than in other deposits.^ Dr Gibson has shown that the manganese nodules from 
these Eed Clays contain a very large number of the rarer metals.® 
Besides the constituents that have just been enumerated, which must be regarded as 
characteristic or essential components of a Red Clay, there are others to be noted that are 
accidental or exceptional. In the Atlantic off the western coasts of Northern Africa, it 
is well known that the Harmattan winds carry at certain seasons of the year large 
quantities of dust far out into the Atlantic Ocean, and in the Red Clays of this region 
these wind-borne particles make up a very appreciable portion of the deposit. In like 
manner the wind-borne particles from the desert regions of Australia can be traced in 
the red clay deposits to the west and south of that island continent.^ There are many 
well-observed instances of volcanic ashes from subaerial eruptions having been carried 
immense distances by the winds before they fell upon the land or the ocean, and we find 
evidence of these in pelagic deposits. It is in every way probable that similar eruptions 
take place under water, and the ashes therefrom are in like manner widely distributed 
over the floor of the ocean.^ We have some excellent examples of these showers of ashes, 
whether from submarine or subaerial sources, on the red clay areas. One of these is 
figured in PI. IV. fig. 3, where the coarser particles have fallen on the Red Clay with 
manganese nodules, and these again have been covered with finer and finer layers of the 
same materials, the whole being solidified into a compact mass, which subsequently has 
undergone great alteration.® 
Among the secondary products arising from the decomposition of the basic volcanic 
rock-fragments present in these deposits are zeolitic crystals resembling in all 
essential particulars, these being especially abundant in some Red Clays from the South 
Pacific and Indian Oceans.® 
Wherever the surface waters of the ocean are affected annually, or occasionally at 
long intervals, by floating ice, the icebergs bear a variety of mineral matters from the 
land of colder latitudes to great distances, and ultimately falling to the bottom they 
form part of the Red Clay and other deposits in great depths. These ice-borne fragments, 
consisting of quartz, felspar, green amphibole, epidote, zircon, tourmaline, &c., and frag- 
ments of ancient continental rocks, such as granite, mica-schist, &c., can be traced in the 
deposits of the Southern Ocean north of latitude 40° S., and in the Western North 
Atlantic they are widespread as far south as the latitude of the Azores. 
In the great majority of the typical Red Clays the size of the mineral particles ranges 
from OT to 0‘85 mm. in diameter, and particles of this size do not as a rule make up more 
than 1 or 2 per cent, of the whole deposit. It occasionally happens that particles larger 
than 0*05 mm. in diameter do not make up as much as 1 per cent, of the deposit. On 
1 See PI. XXIII. = See Appendix II. s See PI. XXVIII. fig. 2. 
^ See PI. XXVI. figs. 2-4 ; PI. XXVII. figs. 2, 3. ® See also PI. XXL fig. 2. “ See PI. XXII. figs. 1-4. 
