582 J- STANLEY GARDINER. 



It is on this sand deposit that the greatest amount of free animal life is fovmd, while 

 sedentary animals tend to settle upon the more current-swept areas. Among the latter forms 

 are certain Polyzoa and Polytrema, which completely grow round small fragments of stone, 

 turning them into more or less round balls, various Alcyonaria, a few sponges and tunicates 

 and corals of such genera as DendrophylUa, Alveopura, Goniopora, etc. Of the free forms 

 in the coral sand small lamellibranchs and gastropods are numerous, as well as young echinids. 

 Crustaceans, particularly Portunidae and Oxystomata as well as Macrura, abound. Certain 

 holothurians, sipunculids and polychaets, as well as Ptychodera and Cephalochorda in certain 

 parts of the shallower waters, are quite numerous. Corals are found only where the sand 

 is moderately coarse, and there is some current, but then such forms as Diaseris, Goniopora 

 stokesi, Heteropsammia and Stephanoseris were remarkably abundant locally. Indeed, dead 

 coralla of the first-named were found to be forming the greater part of a series of con- 

 solidating masses of rock, dredged from an eddy in one of the northern passages of Suvadiva 

 atoll, of which no. 23 was a specimen. 



Lastly, within the most enclosed parts of certain banks and within the lagoons of the 

 deeper atolls a greenish grey ooze, almost a mud, was found (nos. 1 — 10, 20, 21, 24). 

 A similar deposit may possibly have existed in quite shallow water and have been over- 

 looked by us, but, so far as our soundings and dredgings went, there would almost seem 

 to have been a critical depth at about 30 fathoms below which it was for some reason 

 unable to form. It was generally a fairly clean mud, but below 40 fiithoms, when fresh, 

 unctuous, and sometimes smelling slightly of sulphuretted hydrogen. In Suvadiva atoll it 

 was largely coinposed of the shells of Pteropoda, in which connection it is interesting to 

 remark that one morning at the beginning of November, 1899, the water in the lagoon 

 of Goifurfehendu was positively thick with the shells of Clio. Pelagic Foraminifera were 

 common, but bottom-living species were by no means numerous. Sedentary organic life, 

 except sponges, scarcely existed upon it, while free life was only represented by a few species 

 of Crustaceans and a still smaller variety of flat fishes. A holothurian was dredged from 

 this class of bottom (p. 339); it was of peculiar interest on account of the relatively large 

 fragments of coral contained in its gut (no. 25). 



The most interesting point about this muddy deposit from Suvadiva is the presence in 

 it of large quantities of casts of various organisms, more especially Foraminifera. Its minera- 

 logical constituents are small, and are for the most part those found in the open ocean, 

 being of volcanic origin. In connection with this, one may point out that on the shores 

 of many of the islands there are lines of pumice, which the natives state were washed up 

 about 1885, and would hence have probably owed their origin to the eruption of Krakatoa 

 in 1883. In addition half-decomposed pumice is found, in places at some considerable 

 distance inland, which evidently belonged to an earlier period. The analogy between these 

 casts and those of Greensand appears to me to be very close, and I would suggest that 

 here we have an incipient formation of the latter deposit, which is generally supposed to 

 be largely terrigenous in origin. Greensand essentially owes its origin to the filling in of 

 the shells, particularly of the Foraminifera, by a deposit. It was shown in the Challenger 

 Keports to occur between 100 and 900 fathoms along bold and exposed coasts, where pelagic 

 conditions might be expected to closely approach the shores, though all the elements of its 

 •essential constituent, glauconite, may also be present in pumice or the ordinary oceanic, 

 volcanic deposits. That there is any real homology between this deposit and that of Greensand 

 is by no means certain, but, if there be, either the formation of Greensand must depend 

 on physical conditions rather than the proximity of continental land, or Suvadiva atoll at 

 least must have been closely connected with or perhaps founded on the remains of a continental 

 land mass. 



