TEACES OF VOLCANIC ACTION. 261 



limestone mutually exclude eact other. In the border region, 

 about the middle of the group, they are mingled without order ; 

 thus, for instance, the island of Coroere, consisting entirely of 

 tufa, is close to the limestone islands which lie by the southern 

 point of Babelthuap ; then again we find a limestone island, and 

 then the wholly volcanic island of Malacca, and between these 

 larger islands there are numerous smaller ones, some of coral- 

 _ line limestone and some of tufa. 



Yet farther to the south the Andesite and volcanic tufa 

 wholly disappear, and all the islands south of the latitude of 

 Urulong (see Map I.) consist exclusively of upheaved coralKne 

 limestone, partly very highly metamorphosed. These are, with- 

 out exception, true raised reefs, as is seen from their general 

 form, the equal level of their summits, and the fossils found in i 

 their strata ; their structure and their connection with the still/ 

 living reef prove, too, that they are of quite recent origin. It] 

 will be well worth the trouble to study the arguments for thLs \ 

 last statement somewhat more closely. 



The height of the cliffs of the various ' Kokeal ' islands 

 differs greatly ; the highest are from two himdred and fifty to three 

 hundred feet above the sea, the lowest often scarcely ten f eet 

 above the water. Even in the same island, as in Pelelew, this 

 difference occurs. The western cliffs of this island rise to 

 about 250 feet with a perfectly horizontal top ; the eastern cliffs 

 at ArdeloUec, on the contrary, are at most eighty feet above the 

 sea ; their top, too, is almost horizontal. Quite at the south of 

 the island, again, we find cliffs which stand barely five to ten 

 feet above the sand thrown up by the waves. In general the 

 northern islands of the Kokeal are the loftiest ; but even there 

 they certainly never reach' the height ascribed to them by 

 Friedrichsen of from fifteen himdred to two thousand feet. 



The geognostic structure of the Kbkeal islands is also very 

 various. Sometimes the cliffs are composed of very dense 

 limestone in which hardly a trace of fossils can be found, or in 

 which the coralline structure has been preserved ; in the latter 

 case the rock is sometimes hard, as if infiltrated by a dense 

 almost crystalline limestone ; or it may be chalky, as white as 

 snow, and easily friable. The cliffs of Ngaur and Pelelew, 



