16 MR GOODCHILD ON 
quantity of the reef removed in solution. Moreover, it seems 
almost certain that part at least of the dissolved carbonate of 
lime from the surface finds its way downwards in solution 
and is redeposited in the solid form. Furthermore, a certain 
amount of chemical precipitation must arise from the action 
of the waste products of the corals, living and dead, upon 
the sulphate of lime in the sea-water. These causes unite 
to consolidate the lower portion of the reef into one compact 
and nearly homogeneous mass, in which it has long been 
known that little difference of structure can be made out. 
The other compensating cause referred to is that due to 
the action of the breakers, which beat, in many cases, 
almost incessantly, and usually with more or less violence, 
upon the outer margins of the reefs. As a result, large 
quantities of the outer portions of the reef are, from time 
to time, broken off by the waves, and eventually fall imto 
the depths below the outer edge of the reef. There is some 
reason for believing that a steep talus, mainly formed of 
such blocks of broken coral, gives rise to a submarine slope 
below the seaward margin of all coral reefs. As this 
material is considerably augmented by finer coral-detritus, 
and also by the remains of the numerous animals and plants 
living on the reef, by the chemical precipitation just referred 
to, and by the percolation of waters from the surface holding 
lime in solution, the talus is eventually compacted into a 
mass which forms a strong foundation whereon the higher and 
living portions of the reef are enabled to advance seaward. 
Hitherto, and to simplify the case, we have been con- 
fining attention to cases in which the coral reef has grown 
upon a sea bottom which we have supposed to be stationary. 
It may, however, be well doubted whether any portion of 
the earth’s crust is ever really stationary for any length of 
time, geologically speaking. It is almost certain, on the 
contrary, that it is always, more or less, on the move, 
although the rate of movement may be very slow if we 
measure it by the ordinary standards of time. The late 
Charles Darwin thought that nearly all the areas where 
coral reefs occur are areas of subsidence, and in that belief 
the great naturalist has had a very large number of fol- 
lowers. Subsequent investigations, however, especially those 
