256 ELEMENTARY GEOLOGY 
slow and uniform rate; for, if the sinking should become more 
rapid than the rate of coral growth, the animals would soon be 
killed by being lowered into deep water. Professor Le Conte has 
calculated on this theory that there has been a sinking of the bot- 
tom of the Pacific over an area 6000 miles long and 2000 miles 
wide, and that this subsidence has amounted surely to several 
thousand feet, and possibly to as much as 10,000. 
Weare no longer required to believe in this slow and wonder- 
ful sinking of the sea bottom, for it has been shown that the atolls 
are capable of other explanation. Briefly stated, the new theory, 
which has been chiefly advocated by Professor Murray, is that the 
corals start their growth on some platform below the sea-level, 
and that upon this a reef is built. This growth may commence 
on the side of a volcanic cone, or mountain peak, which may 
either rise above the surface, or be entirely submerged. The 
bottom of the ocean may be rising, or sinking, or even remaining 
perfectly quiet. 
Therefore, according to this, it is possible to accept the Darwin 
explanation for some of the atolls, while for others we may rely 
upon an entirely different theory. The Murray theory certainly 
explains some atolls, and other kinds of coral reefs, that have been 
shown to be developing where the bottom of the sea is actually 
rising instead of sinking, as is required by the Darwin theory. 
Probably both explanations are needed to account for all reefs. 
Variation of Sediment from the Shore to the Deep Sea. 
— Mechanical Sediments. At the very coast line the 
sediments are naturally coarse, though as has been 
stated, in some places they are comparatively fine in 
grain. Since the transportive power of the waves 
and currents decreases in deeper water, only the 
lighter fragments can be carried out to sea. 
Still, for a distance of several miles from the coast, 
