BY H. B. GUPPY, M.B., SURGEON, R.N. 959 



An apparent objection here presents itself with reference to the 

 last two conclusions. If reefs begin to build their foundations in 

 dejiths greater than those which are usually assigned to them, the 

 thickness of the elevated coral formations I examined ought to 

 have been far in excess of a hundred feet. But fringing reefs 

 themselves are restricted to shallow waters around the coast, and 

 their seaward extension in localities where the submarine slope is 

 steep must be extremely slow. Whilst, on the other hand, in an 

 area of elevation, such as that in which the Solomon Islands are 

 included, barrier-reefs, which begin to grow in depths not less 

 than fifty fathoms, may owe their approach towards the surface as 

 much to the elevating movement as to the verv slow upward 

 growth of the coral. It should also be borne in mind that the 

 rapid subaerial denudation to which these regions of heavy rainfall 

 are subjected would be an important agency in the thinning away 

 of the raised coral formations. 



In conclusion I may observe that the preceding remarks, 

 although in the main suggestive, are founded on observations not 

 only of reefs as they skirt a coast, but of those whose foundations 

 have been exposed by upheaval. After having failed to account 

 for the oi'igin of the barrier-reefs of Bougainville Straits by the 

 views at present held of the growth of coral reefs, I offer the 

 foregoing explanation of their formation. 



