262 THE INFLUENCE OF INANIMATE SURROUNDINGS. 



for instance, consist of such a snow-white rock, and their 

 gleaming perpendicular walls form a landmark from afar for 

 the sailor. The masses of fossils found in them, both corals and 

 shells, are for the most part merely impressions preserved in the 

 limestone. This is difficult to detect at the first glance ; for the 

 corals especially, or rather their impressions, lie so wonderfully 

 closely that they seem to form a dense mass of compressed 

 corals. 



The geographical distribution of these different kinds 

 of coralline limestone also offers some striking peculiarities. 

 All the Kokeal islands which I saw, and which lay in the 

 vicinity of volcanic rocks as, for instance, thote in the neigh- 

 bourhood of Coroere consist of dense limestone which is often 

 semi-crystalline; when fossils occur, they are firmly imbedded in 

 the rock and preserved uninjured. These islands also yield 

 exclusively the large pebbles of arragonite which are used by the 

 natives of the island of Yap lying a hundred miles to the 

 northward as a kind of money in great request. The more 

 remote the islands are from the centre of volcanic action 

 presumably situated in the middle of Babelthuap, the less 

 prevalent is the limestone, dense or crystalline, till in the 

 south it finally quite disappears. 



The fossils contained in these rocks show, in conjunction 

 with other peculiarities in the structure of the xipheaved reefs, 

 that these reefs belong to quite a recent period, and that, in 

 fact, we must regard them only as the beginning of the reefs 

 now in course of construction in the neighbouring seas. On the 

 island of Noerkessul, lying on the eastern reef of Pelelew, 

 which is only about twenty to twenty-five feet high, I found 

 with true Astr^idae, imbedded in the rock, a tooth of the 

 Indian crocodile, which still is found there, though it is not 

 frequent. On the little island of Calacoligoll, which is almost 

 on the outer ridge of the western reef of Pelelew (that is to say 

 not more than 120 feet from it), I found a large block, at least 

 five feet in. length, in which the imbedded corals stood upright, 

 and among them were shells of Pholas and numerous tubes of 

 Vermetus gigas, which still lives and is very common in the 

 sea close by. The centre of Pelelew is from twenty to twenty- 



