254 THE INFLUENCK OF INANIMATE SUEROUNDINGS. 



numbers of narrow canals with jjerpendicular sides, usuallj' 

 from two to three fathoms deep or even more, and evidently 

 cut into the stone by the action of currents ; they grow deeper 

 and broader to the east and north-east, and there ultimately fall 

 into a wide basin, extending as far as the south point of Eabel- 

 thuap, and between fifteen and twenty-five fathoms deep. The 

 rise of this limestone bottom, is just as gradual towards the 

 outer reef — where it appears as its internal declivity — as its 

 slope where it forma the I'ocky islands ; still it nowhere consti- 

 tutes any portion of the present living reef. These conditions 

 are very difficult to explain by the hypothesis of recent sub- 

 sidence. If such a process had in fact and exclusively effected 

 the submergence of the limestone plateau, this must have ac- 

 quired its peculiar structure before this recent subsidence was 

 initiated, which is in itself highly improbable. The whole 

 plateau, on the contraiy, with its channels, prodices the im- 

 pression that it has been recently formed during a period of 

 rest or of slow elevation. But the limestone plateau affords 

 even better arguments against the assumption that subsidence 

 was going on during the formation of these reefs. Wherever 

 the limestone islands of the southern legion are exposed to the 

 denuding action of the rising tides, a wall like a hollow cornice 

 rises abruptly froui the base of the island which slopes up 

 gi-adually from the submarine level, and its summit, which 

 often overhangs to a dangerous extent, has a growth of shrubs 

 or trees. This hollowed-out base, which would show a highly 

 conca.ve section, is from six to ten feet high ; at the highest 

 flood-tides the water rushes into it with great force, and its 

 face exhibits many smaller holes and fissures, often eaten into the 

 solid rock for some feet. In many spots the overhanging sum- 

 mit threatens to fall, and that such catastrophes are certainly 

 not rare, may be seen 1 ly the piled-up fragments which in many 

 places lie .half in the water at the foot of the islands. This 

 seems to me to prove convincingly that a subsidenc(! has not 

 taken place, for it is not clear how, during subsidence, such a 

 form of the internal limestone plateau and its transition into 

 the islands rising from it could have originated. 



It might, however, be conceded that the phenomena here 



