66 GEOLOGICAL DISTRIBUTION. 
CHAPTER VIII. 
GEOLOGICAL DISTRIBUTION. 
“THE past history of animals might conceivably have 
been a sealed book to man’s investigations but 
fortunately the succession of organisms has left considerable 
vestiges behind it. These vestiges, in a general way, are 
termed /ossi/s, which are mostly found deposited in earth. 
The surface of the earth for a slight but varying depth 
consists of a loose soil, but below this there are layers or 
strata, formed of various substances, such as limestone, 
sandstone, coaland so on. These strata have been gradually 
deposited in past ages by the action of natural forces. At 
the present time the same process is going on. The dry 
land is slowly being broken up by the action of rain, frost 
and other agencies, and the finely divided remains are being 
carried out to the sea by rivers. There the sediment in the 
form of mud and sand is slowly deposited on the sea-floor. 
All along the sea-coasts the waves are ceaselessly carrying 
on the same work of destruction, the pebbles, sand and 
mud being deposited out to sea. Hence the physical 
agencies of wind, tide, rain and wave work to a common 
end—the reduction of the earth’s surface to a dead level 
which, if ever attained, will be some feet below the general 
surface of the sea. At present there is a counteracting 
force to the attainment of this in the elevation of the earth’s 
surface by the active agencies in its interior. : 
We must therefore conceive of the whole of the earth’s 
surface as a shifting scene of land and water, upon which 
the levelling and elevating agencies are constantly at work 
in opposite directions. Should the elevating agencies, due 
