AGASSIZ: FIJI ISLANDS AND CORAL REKFS. 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 coi'al 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. N ullipores, 

 Algae, Corallines, Foraminifei-a, the minute fragments of corals or small 

 particles of sand, all continue to act as gi'eat 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 iu 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 hufre 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.^ 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 f;\r beyond those at which so called reef builders flourish." 



1 Bull. IMus. Comp. Zool., Vol. XVIL No. S, April, 1889, p. 121. 



2 Pourt.iles, Mem. Mus. Comp. ZooL, Vol. XL No. 2, 1871; Wyville Tiiomson, 

 Depths of the Sea, 1873, p. 432 ; also The Voyage of the Challenger, the Atlantic, 

 1877, Vol. L pp. 266-273. 



