Submerged Valleys and Barrier Reefs

Abstract

IN a letter on “Dana's Proof of Darwin's Theory of Coral Reefs”, published in NATURE for April 3, Mr. Cyril Crossland points out that “land valleys which extend beneath the sea are not always proof of subsidence. Such valleys, like coral reefs, may owe their existence to different factors in different tases”. He adds that certain harbours on the east coast of Africa “are the high parts of submarine fault valleys”, which, although they simulate embayments produced by the general depression and partial submergence of a dissected coastal region, really result from the local depression of fault blocks, and hence cannot be taken as evidence that any coral reefs which may occur near them have been built up during a period of submergence.