of Edinburgh, Session 1883-84. 
521 
and delicate, and, for the quantity of carbonate of lime present, 
offer a larger surface to the action of the solvent than the thicker, 
though smaller, Glohigerina shells, we shall see the explanation of 
this apparent anomaly. 
It remains now to point out the area occupied by the red clay. 
We have seen how it passes at its margins into organic calcareous 
oozes, found in the lesser depths of the abysmal regions, or into the 
siliceous organic oozes or terrigenous deposits. In its typical form 
the red clay occupies a larger area than any of the other true deep- 
sea deposits, covering the bottom in vast regions of the North and 
South Pacific, Atlantic, and Indian Oceans. As above remarked, 
this clay may be said to be universally distributed over the floor of 
the oceanic basins ; but it only appears as a true deposit at points 
where the siliceous and calcareous organisms do not conceal its proper 
characters. 
Having now indicated its distribution, we must consider the mode 
of its formation, and give, in addition, a concise description of the 
minerals and of the organic remains which are commonly associated 
with it. The origin of these vast de]30sits of clay is a problem of the 
highest interest. It was at first supposed that these sediments were 
composed of microscopic particles arising from the disintegration of 
the rocks by rivers and by the waves on the coasts. It was believed 
that the matters held in suspension were carried far and wide by 
currents, and gradually fell to the bottom of the sea. But the uni- 
formity of composition presented by these deposits was a great objec- 
tion to this view. It could be shown, as we have mentioned above, 
that mineral particles, even of the smallest dimensions, continually 
set adrift upon disturbed waters must, owing to a property of sea 
water, eventually be precipitated at no great distance from land. It 
has also been supposed that these argillaceous deposits owe their origin 
to the inorganic residue of the calcareous shells which are dissolved 
away in deep water, but this view has no foundation in fact. Every- 
thing seems to show that the formation of the clay is due to the 
decomposition of fragmentary volcanic products, whose presence can 
be detected over the whole floor of the ocean. 
These volcanic materials are derived from floating pumice and 
volcanic ashes ejected to great distances by terrestrial volcanoes, and 
carried far by the winds. It is also known that beds of lava and of tufa 
