Geologij. 289 



of Murray Hill, Phosphate Hill, and the highest land over Plying 

 Fish Cove are dolomitic limestones, containing 34 to 41 per cent, 

 of carbonate of magnesia. Descriptions and analyses of these rocks 

 (jN'os. 378, 514, 800, 811) are given above by Mr. E. W. Skeats 

 (pp. 267-268) ; and Messrs. Jones & Chapman have described the 

 organisms contained in 378 (p. 257) and 800 (p. 258), and also 

 in 1^0. 143 (p. 256), a similar rock from the summit of Eoss Hill. 

 In all cases the fossils are nearly obliterated, and only imperfect 

 remains of a few foraminifera and fragments of Lithothamniony 

 which resists destruction to the last, are to be seen : in the rock 

 from Murray Hill there may be traces of coral structure. The 

 rocks forming the rim between the hills are of a similar character 

 both on the seaward side and on the landward slope, or low cliffy 

 which, according to the view expressed above, faced the lagoon. 

 In these, although their general appearance and mode of occurrence 

 point to an origin from a coral reef, yet traces of coral are rarely 

 seen. In some places, where the limestones contain little carbonate 

 of magnesia, the foraminifera are fairly distinct : an example of 

 such a rock is IS'o. 134 (pp. 256 and 265), which was collected 

 a little below the summit of the upper cliff on the east coast. 



The rocks of the central plateau have been examined only in 

 part. One of the most interesting is from pinnacles projecting 

 from the soil at about 800 feet above the sea (Ko. 935, p. 257) : 

 it is a crystalline limestone crowded with fragments of LitJiothamnion 

 and Halimeda, together with a few foraminifera, and it seems 

 to be a shallow-water rock, such as might well accumulate in 

 a lagoon. At no great distance from this there is another rock 

 which points more strongly to lagoon conditions. This is a fine 

 white limestone, which for the most part is of a powdery chalk-like 

 consistency, is composed entirely of carbonate of lime, and usually 

 contains no organisms : scattered in it are irregular hardened masses 

 which include numerous foraminifera, which are described above 

 (jS^o. 658. p. 257) as being undersized and thin-shelled, and the 

 nature of the rock as a whole is stated to indicate that it was once 

 the soft mud of a shallow lagoon, an interpretation which the 

 position in which it is found strongly supports. Some of the hard 

 masses closely associated with this rock are dolomitized and the 

 organisms obliterated. (See Ko. 658, p. 268.) 



The most important evidence that the higher points on the 

 northern and eastern rim of the plateau once formed islets is 

 the existence upon several of them of thick beds of phosphate 

 of lime, for it is difficult to account for the great accumulation 

 of this substance at these points otherwise than by supposing that 

 it is derived from thick beds of guano deposited on these elevations 

 under conditions very different from those now prevailing. The 

 necessary conditions would seem to have been fulfilled if these 

 hills formed low treeless islets, whether these consisted merely 

 of accumulations of coral thrown upon the reef by the action of 

 the waves, or were the highest points along the line of reefs which 



