THE MAEQUESAS. 5 



southeast and northwest spits, where the promontories of the islands 

 extend seaward as shallow points, on which corals have established 

 themselves. It is also possible tliat the successive flows of lava from 

 Mehetia and the extinct craters of the Marquesas may have destroyed 

 the corals or prevented their obtaining a foothold. Corals occur only 

 in patches in the Galapagos Islands, in a still active volcanic district, 

 where their development should be most favored, judging from the 

 oceanic conditions existing there, and where tliere is no trace of any 

 subsidence having occurred. 



Dana and Darwin have supposed that the absence of corals on these 

 islands was duo to their having gradually subsided, yet subsided so fast 

 that corals were not able to find a footing on their steep slopes. 

 Daua^ also attributes the absence of corals in tlie Marquesas to the 

 depth of water about the islands in addition to subsidence ; he says in 

 substance, if before the subsidence there was some extent of shallow 

 water round an island, it might have had very bold shores after it had 

 half sunk beneath the waves. The Marquesas may therefore have had 

 barrier reefs which were sunk from too i-apid subsidence ; others again 

 failed to form on account of deep water near the shore. There are, as 

 I have stated, no indications that either the Marquesas or Mehetia has 

 been subjected to the effect of subsidence, as Dana assumes. 



The soundings which we took (PI. 200, stations 24, 25, 26, 27, 28) 

 indicate that there is a ridge gradually rising from a depth of about 

 2100 to a depth of about 800 fathoms, which connects Ua Huka and 

 Nukuhiva (Fig. 1), but existing soundings do not indicate what con- 

 nection (if any exists) there may be between the other islands of the 

 group. 



It is not vmcommon to find volcanic islands with in.sig-nificant frinsj-insj 

 reefs, or with only patches of fringing reefs, in regions where other vol- 

 canic islands have well-developed barrier and fringing reefs due to the 

 existence of more or less wide platforms of submarine erosion. I 

 might mention the Home Islands (A. Chart 987), not more than 90 

 miles distant from the Fiji group ; both volcanic groups, the former 



' Dana, Corals and Coral Islands, 3d edition, 1890, pp. 340, 361. 



