Vol. 54.] OH" CLIPPEETON ATOLL. 229 



of the volcanic base on the rim alone be explained. If the island 

 has sunk, why is it not, as in all other cases, in the lagoon ? 



If the coral circle has ^rown up on the flanks of the original 

 volcanic mound, the same difficulty presents itself. Unfortunately 

 we know nothing of the depths around ; and it is only on the some- 

 what vague soundings of the lagoon by the captain of a merchant 

 vessel that the plan is based, showing that the depths there are very 

 considerable, amounting to 50 fathoms. 



If this be so, it adds another peculiarity to the atoll, for in no 

 known case is so great a depth found in so small an atoll. 



On this point Mr. Arundel writes as follows : — 



' After taking soundings in a perfectly round hole in the lagoon, 

 which looks very much like an old crater, and where we obtained 

 as much as 20 fathoms (a man named Antone claims to have got 

 soundings at 2Q fathoms), we started to the north-western side of 

 the island. On the way from the circular basin, we took another 

 sounding in what looked like a deep part, but only obtained 11 

 fathoms.' 



The true greatest depth is thus doubtful ; but even 20 fathoms 

 is deep for so small an atoll. 



The only solution which presents itself to me is that we here 

 have the rare case of coral forming on the lip of a volcanic crater, 

 one part of which alone, perhaps the plug, has resisted the action of 

 the sea, which has worn the rest of it down to the limits of wave- 

 action. 



It will be remembered that the great explosion of Krakatoa 

 resulted in the blowing away of a large part of the island situated 

 above the hollowed-out interior, but that the margin of the actual 

 vent remained on one side of the deep hole thus formed. 



A similar incident, leaving a plug on one side of the crater-hollow, 

 might explain the Clipperton Eock. 



EXPLANATION OE PLATES XX-XXII. 



Plate XX. 

 Map of Clipperton Atoll, reduced from the new Admiralty chart. 



Plate XXI. 



View of the rock on Clipperton Atoll, looking north-west. (From a 

 photograph.) 



Plate XXII. 



Nearer view of the same rock. (From a photograph.) 



Q. J. G. S. No. 214. E 



