THE ORIGIN OF CORAL REEFS. 5S 
the waves, hollow out a basin surrounded by a margin of 
living coral. In this manner a miniature atoll is produced. 
In 1870 Dr. Rein appeared in the field as a supporter of 
the view that the forms of reefs are due to the natural growth 
of corals. The Bermudas he regarded merely as portions of 
a large atoll crowning a submarine bank.* 
In 1880 Mr. John Murray published his theory of the origin 
of coral reefs.+ Though placed in direct antagonism to the 
accepted theory of subsidence, it was in no way a change of 
front, if we view it in the hght of the researches made 
within the previous thirty years. The new view, in supply- 
ing a foundation for atolls without the aid of a sinking move- 
ment, filled up the great gap in the original explanation of 
Chamisso, a point of weakness, which, it will be remembered, 
led Mr. Darwin to his theory of subsidence. It had been 
previously shown by Agassiz and Pourtales, in 1871, that on the 
surface of the Pourtales Plateau in the Florida Seas, at a depth 
of from 100 to 250 fathoms, there was a great abundance of 
deep-sea corals and other organisms by which a modern coral 
limestone was being formed.{ Mr. Murray, with all the facts of 
the explorations of the Challenger at his disposal, showed that 
in tropical seas submerged banks and plateaux are continually 
in process of formation, by the rapid accumulation of the 
shells, skeletons, and other hard parts of the organisms that 
flourish in great numbers and variety on their summits. Sub- 
marine volcanic peaks could in this manner be levelled up to 
the zone in which the ordinary reef-corals thrive, and ulti- 
mately the coral atoll would appear at the surface. This I hold 
to be the important feature of Mr. Murray’s theory, and for 
these two reasons. It filled up the great gap in that explana- 
tion of the origin of coral reefs, which ascribed their forms to 
their mode of growth. It has been remarkably confirmed by 
more recent researches and discoveries in the Florida Seas 
and in the Western Pacific. The forms of reefs Mr. Murray 
ascribed to well-known physical causes, concerning which 
later observers only differ as to the importance they would 
attach to each particular agency. Atolls, he says, owe their 
form to the more abundant supply of food to the outer margins 
and to the removal of dead coral rock from the interior por- 
tions by currents and by the dissolving action of the carbonic 
acid of the sea-water. Barrier-reefs have built out from the 
shore on a foundation of volcanic débris, or on a talus of coral 
* Bericht Senckenberg, Naturfersch. Gesellsch., 1869-70, p. 157. 
+ Proc. Roy. Soc. Edin., 1879-80. 
{ Illustr. Catal. Mus. Compar. Zool., 1871. 
