590 PROCEEDINGS OF THE AMERICAN ACADEMY, 



of all rock-building organisms, even at the extreme depth of 1120 feet, a 

 depth of course well within their ordinary bathjmetric distribution, as 

 shown by the Pourtales Plateau. Apart from the considerable amount 

 of material which they may add to any shoal, the great importance of 

 the incrusting nullipores lies in their solidifying and cementing action. 

 Thus, on the sea face of a reef, they are most effective in protecting it 

 against the force of the surf, as, for example, in the case of the Bermuda 

 serpuline reefs, a function which they share chiefly with the tube-building 

 annelids. In the upbuilding of submarine banks they carry on a very 

 similar process. The events now going forward on the Challenger Bank 

 are probably as follows. The nullipores gradually form incrusting masses 

 about various objects, or grow up independently on stalks which later 

 become broken ; in these ways the spherical concretions begin. Lying 

 free on the bottom, subject to the action of the waves, they are occasion- 

 ally turned during their growth so that they retain a spheroidal form, 

 until at last they can no longer readily be moved ; whereupon, lying 

 motionless side by side, they become cemented together by the incrusting 

 organisms, and thus come to form a solid modern limestone, which is 

 produced much more rapidly than that which is formed from the loose 

 shell sands. This process taking place over the Challenger Bank, where 

 there is no direct evidence of either elevation or subsidence, has raised 

 it to within some thirty to fifty fathoms of the surface of the sea; a 

 deptli where a few corals already flourish. If we imagine this process 

 as continuing until the bank rises to within about twenty fathoms of the 

 surface, we should then have excellent conditions for the formation of a 

 coral reef. Of course in such upbuilding the nullipores constitute only 

 a part, though a most important one, of the, whole growth ; the tests of 

 Forarainifera, and the remains of other lime-secreting organisms, add 

 largely to the accumulation of material. 



The reports of the borings in Funafuti, a true coral island of the Fl- 

 lice group, recently published (Bonney and others, :04) by the Royal 

 Society of London, are of special interest in this connection. After two 

 unsuccessful attempts, the drill was finally driven to a depth of 1114 

 feet, and the cores have since been carefully studied. Dr. G. J. Ilinde 

 has given (pp. 18G-3G1) an elaborate account of the organisms; and the 

 evidence goes to show that whether in the form of solid rock cores, or 

 as incoherent gi-anular particles, the material is entirely of organic char- 

 acter, traceable to the calcareous remains of animals and algae, of which 

 Halimeda and Litliothamnion occur in greatest abundance. Professor 

 Judd remarks that " from toj) to bottom the same organisms occur. 



