214 Claypole on (Darwin and Geology. 
single instance has any trace been found of a sunken mountain 
peak as the base of a coral islet, (for oceanic islands are uni- 
formly volcanic,) Mr. Murray proposes as the foundation of his 
theory, the elevation of the^iigher portions of the sea-bottom by 
deposition of organic material or by volcanic action, until they 
come within the limit of reef-forming polyps. Then the prin- 
ciples already mentioned, of faster grow^th on the margin and of 
death and erosion in the center, vsill do all the rest and produce 
in time the fringing reef and the atoll. 
Though it is obvious that Mr. Murray's theory gains enor- 
mously by being free from the fundamental objection to that of 
Darwin, and is strong just where the latter is weak, yet it 
would be premature to say that it has yet found general accept- 
ance. The geological world is divided, as is conclusively 
shown by the controversy above alluded to, and this is not the 
place for the expression of individual opinion. Both may be 
true in different places.^ 
It should however be mentioned that in another point the 
later theory enjoys a considerable advantage over the earlier. 
The unfathomable depth of water so often reported close to 
the edge of a reef was evidently a natural and necessary con- 
sequence of its mode of formation according to Darwin. But 
this depth seems from recent soundings to be fictitious or at 
least non-existent. The edge of the reef, it is true, falls off to 
seaward very steeply for a short distance, after which there fol- 
lows a gradual slope not exceeding six degrees of inclination, 
and just' such as might be looked for on a submarine bank. 
This bank at no very great distance from the reef ceases to be 
composed of coral and yields to the dredge nothing but vol- 
canic dust, apparently the comminuted ejecta of some subma- 
rine vent. 
Passing from this topic of coral formation M'here we find 
Darwin invoking the most extensive subsidence, in time com- 
paratively recent, that has perhaps ever been suggested, it is 
not a little interesting and certainly amusing to note the indig- 
^ A good summary of the two theories and mvich other interesting 
material of a kindred nature may be found in "Nature" for November, 
1883, from the pen of Dr. Arcliibald Geikie. 
