June, 1906. New Forms of Concretions — Nichols. 41 



It was the opinion of "James D. Dana* that these two banks were, 

 in comparatively recent historical times, islands, which were even 

 mapped as "The False Bermudas." Early accounts of these banks 

 described them as "rocky ledges, "f The ship Challenger visited the 

 bank of that name upon the 23d of April, 1873. Upon its map of the 

 region+ the character of the bank is given as coral. Sir C. Wyville 

 Thompson,§ who was with the Challenger expedition, says: "The 

 bank, which seems to be about five miles across, consists mainly of 

 large rounded pebbles of the substance of the Bermuda serpuline reef. 

 There is an abundant growth all over the pebbles of the pretty little 

 branching corals, Madracis asperula and M. hellana. " He mentions 

 also that starfish and other animals were brought up in the dredge. 

 Mr. Bean, dredging in 28 fathoms, found that the bottom was 

 covered with the nodules under consideration, which are doubtless 

 identical with Sir Wyville Thompson's pebbles. The nodules were, 

 however, imbedded in calcareous ooze, and although covered by 

 living forms, the branching skeletons, which may well correspond 

 with Madracis, appear from inspection of the dried specimens to 

 have been dead sufficiently long to become encrusted with bryozoa 

 and nullipora. 



If these nodules are rolled fragments of serpuline limestone, both 

 the existence within a few hundred years of the False Bermudas and 

 their extremely rapid subsidence is as good as proven. The three 

 and one half miles of deep sea which separate the banks from the 

 nearest reefs offer an insuperable obstacle to the transportation of 

 pebbles in such large numbers. Such nodules of fragmental origin 

 also could not form in situ under present conditions, for wave action 

 at depths of twenty-four to thirty fathoms is either very weak or 

 entirely lacking. The current of three knots has not sufficient 

 power to round boulders of such size. If, however, they are 

 accretions, they have little or no apparent bearing upon these ques- 

 tions, and the interest in them arises from other sources. 



The nodules from the Challenger bank (Plate XXV) in the 

 possession of the Museum were dredged, as already stated, from a 

 depth of about twenty-eight fathoms. The nodules are roughly 

 spherical, with pitted and irregular surfaces. When collected, they 

 were covered with living hydrozoa, other animal forms and algae. The 



♦Corals and Coral Islands, p. 187. 



tlbid. 



JChallenger Report: Narrative : Vol. I, facing p. 149. 



SVoyage of the Challenger : The Atlantic, Vol. I, p. 333. 



