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AGASSIZ: FIJI ISLANDS AND CORAL REEFS. 87 
reef flats wherever they have been examined by means of the sounding 
lead, the dredge, the tangles, and the water glass, identical results have 
been obtained as regards the bathymetrical range of the reef growing 
corals, with the exception that the lower limit of depth seems to be 
somewhat greater, and extends in some instances to 17 or perhaps even 20 
fathoms. We should also remember that there abound on all coral reefs 
numberless organisms whose only role seems to be to cement again the 
particles and fragments broken by the action of the sea or of boring 
animals, and they play a most important part in forming coralline lime- 
stone full of reef building corals, which yet have nothing to do with the 
increase of thickness of the reef from their own growth. Nullipores, 
Algze, Corallines, Foraminifera, the minute fragments of corals or small 
particles of sand, all continue to act as great cementers at considerable 
depths far beyond that at which reef building corals have ceased to 
flourish. They act not only on the surface of the reef in the interior of 
the lagoons, but along its sea face and down to a considerable depth, 
and all along the outer slope they cement the fragments of corals 
which have fallen at the foot of the growing reef, and gradually trans- 
form the material of the talus into a hard limestone similar in its 
constitution to that of the reef building corals. But in this lime- 
stone formed of talus material, the corals no longer retain their natural 
attitude as when growing. It is a breccia of corals or a puddingstone, 
consisting sometimes of huge masses which have fallen from the 
growing face of the reef and rolled upon the talus along the sea 
slope where such a conglomerate breccia or puddingstone has been 
formed, and it reaches the depth of from 15 to 20 fathoms. Corals 
can again grow upon this buttress, and thus we may imagine the 
reefs of the present day to build outward and increase in thickness. 
This was the result which was hinted at from an examination of the 
sea face of the reef off Honolulu made in 1888.1 Of course I do not 
deny that some reef builders may occasionally live at greater depths than 
those I have mentioned, but their casual occurrence at those greater 
depths would not materially affect the growth in height and increase in 
width of the great majority of coral reefs ; and it is well known that 
Oculina, Lophohelia, and other genera, may cover extensive tracts at 
depths far beyond those at which so called reef builders flourish.’ 
1 Bull. Mus. Comp. Zodl., Vol. XVII. No. 3, April, 1889, p. 121. 
? Pourtalés, Mem. Mus. Comp. Zodl., Vol. II. No. 2, 1871; Wyville Thomson, 
Depths of the Sea, 1873, p. 482; also The Voyage of the Challenger, the Atlantic, 
1877, Vol. I. pp. 266-273. 
