625 
follow, whieh will serve to some extent to test its probability. Some 
of these may be briefly mentioned here. 
When a voleanic island, crowned with some form of reef struc- 
ture sinks down, it may happen, as has been stated above, that the 
upward growing reef-building corals do not succeed in the long run 
in keeping in contact with the superficial layers of the ocean which 
alone present the conditions necessary for their existence. As soon 
as they have sunk down below the limit of depth down to which 
reef-building corals can live, they will no longer be able to grow 
further but together with their basement of volcanic origin they 
will continually sink deeper and die off. If this be true we may 
expect to find such sunken reefs at very different depths within the 
area of the reef-building corals. As far as I know, it has never 
been described up to the present that in the Pacific fragments 
of reef-building corals have been dredged from great depths 
which could not in all likelihood be considered as originating from 
neighbouring coral islands rising above the sea. But this cannot be 
wondered at since the number of deep-sea dredgings is not large 
and next to nothing when we think of’the extensive area we have 
to deal with, so that the chance must be extremely small, that a 
point where portions of a drowned coral-reef occur, will be hit 
exactly. Outside of the Pacific, however, viz. in the Ceram Sea, a 
fact’) has occurred which I consider very important. 
I mean the dredging No. 177, made on Sept. 1, 1900, by the 
Siboga *) in the middle of the Ceram Sea *). From a depth ranging from 
1633 to 1304 m. over a distance of no less than three nautical miles 
large quantities of recent reef-building coral were then dredged, which 
1) After this paper had been read, a second instance came to my notice through 
the courtesy of Mr. J. W. van Nounuys, who informed me, that in the year 1914, 
when commanding the ship Telegraaf of the Government Navy in the Netherlands 
East Indies he brought to the surface from a depth of 1500 m. some pieces of 
coral reef limestone at a spot, situated about 30 nautical miles from the nearest 
shore, of the island of Engano. The exact spot where this deep-sea sounding took 
place is 5°33’ Lat. and 102945’ Long. 
2) It is also possible that similar finds have been been made elsewhere by deep-sea 
expeditions but have not been recorded. Very remarkable are the results obtained in 
the year 1899 by the steamer Albatross at the stations Nos. 35, 489 and 112 
near. the Paumoto archipelago, where from depths of 1462, 1125 and 1568 fathoms 
resp. socalled coral sand was dredged; no coral islands lie at a smaller distance 
from there than 4/3 degree latitude. 
A. Acassiz. The coral reefs of the tropical Pacific p. 25, fig. 2 and Plate 201. 
Mem. of the Museum of compar. Zoology at Harvard College XXVIII, 1915. 
3) See Siboga expedition, Vol. I. M. Weger. Introduction et description de .’expé- 
dition p. 80, 1902. max, 
