12 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
for the breakers cannot cut on the shores of the island,’ and they do not 
often tear up and cast inside fragments from the outer edge of the reef, 
while every streamlet carries away its mud through breaches in the 
reef... . A fringing reef, if elevated in a perfect condition above the 
level of the sea, would present the singular appearance of a broad dry 
moat bounded by a low wall or mound.” 
Darwin, when meeting Semper’s objection that the existence of atolls 
or barrier reefs in a region of elevation was a fatal argument against 
his (Darwin’s) views, is obliged to say that therein “seems to me no 
improbability in their having originally subsided, then having been up- 
raised . . . and again having subsided.”? He further says, “ The exist- 
ence of atolls and of barrier reefs in close proximity is manifestly not 
opposed to my views.” Certainly not, but their existence in an area of 
elevation as claimed by Semper is. Darwin also says that, ‘‘ When the 
land is prolonged beneath the sea in an extremely steep slope, reefs 
formed there during subsidence will remain closely attached to the 
shore, and will be undistinguishable from fringing reefs.”* This seems 
to me impossible. The disintegration of the inner edge of the fringing 
reef, the action of the sea upon this disintegrated material, the solvent 
action of sea water, all will tend to form a channel between the outer 
parts of the reef and the shore, as is evidently the case in almost all 
fringing reefs, which show either an incipient channel where boats may 
circulate at high water, or a belt of considerable width in which the coral 
fringing the land has been killed by the silt brought down from the ad- 
jacent slopes, and has been decomposed, and, crumbling to sand or mud, 
is gradually being carried off at each high tide, forming a channel which 
when wide enough and deep enough becomes sufticiently prominent to 
change the fringing reef into a barrier reef. 
The difficulties encofntered in attempting to meet the many sugges- 
tions made by Darwin regarding reefs which he did not examine are 
well exemplified in the account which he gives of Rose Island, one of 
the Samoa group. 
1 This Yould depend upon the width and slope of the fringing reef. Many of 
the narrow fringing reefs in Fiji have a uniform slope towards the lagoon, and do 
not present the structure described by Darwin. 
2 Darwin’s Coral Reefs, 3d ed., p. 228. 
8 Ibid., p. 229. 
4 Tbid., p. 212: “The lagoon is very shallow, and is strewn with numerous large 
boulders of voleanic rock.” (Negro-heads, A. Ag.) He further says: “ This island, 
therefore, probably consists of a bank of rock, a few feet submerged, with the 
outer margin fringed with reefs. Hence it cannot be properly classed with atolls, 
