502 
Froceedings of the Royal Society 
go to the formation of deposits in the deep water immediately 
surrounding the land and in the truly oceanic areas, attention 
must now be directed to the agents which are concerned in the 
transport and distribution of these, and to the sphere of their action. 
The relations existing between the organic and inorganic elements 
of deposits to which we have just referred, and the laws which 
determine their distribution, will be pointed out at the same time. 
The fluids which envelope the solid crust of the globe are in- 
cessantly at work disintegrating the materials of the land, which, 
becoming loose and transportable, are carried away sometimes by 
the atmosphere, sometimes by water, to lower regions, and are eventu- 
ally borne to the ocean in the form of solid particles or as matter in 
solution. The atmosphere when agitated, after having broken up 
the solid rock, transports the particles from the continents, and 
in some regions carries them far out to sea, where they form an 
appreciable portion of the deposit ; as, for instance, off the west 
coast of Xorth Africa and the south-west coast of Australia. Again, 
in times of volcanic eruptions, the dust and scoria which are shot 
into the air, are carried immense distances by winds and atmo- 
spheric currents, and no small portion eventually falls into the sea. 
Water is, however, the most powerful agent concerned in the 
formation and distribution of marine sediments. Running water 
corrodes the surface of the land, and carries the triturated fragments 
down into the ocean. The waters of the ocean, in the form of waves 
and tides, attack the coasts and distribute the debris at a lower 
level. Independently of the action of waves, there exist along 
most coasts currents, more or less constant, which have an effect in 
removing sand, gravel, and pebbles further from their origin. 
Generally, terrestrial matters appear to be distributed by these means 
to a distance of one or two hundred miles from the coast. Waves 
and currents probably have no erosive or transporting power at 
depths greater than 200 or 300 fathoms, and even at such depths 
it is necessary that there should be some peculiar configura- 
tion of the bottom in order that the agitated water may produce 
any mechanical effect. However, it is not improbable that, by a 
peculiar configuration of the bottom and ridges among oceanic 
islands, the deposit on a ridge may be disturbed by the tidal 
wave even at 1000 fathoms; and this may be the cause of the hard 
