230 /. D. Hague on the Guano Islands of the Pacific Ocean. 



had long been covered up under the deposit and in some of which 

 the ctirbonic acid had been almost entirely replaced by phos- 

 phoric acid. In such I have found seventy per cent phosphate 

 of lime. In many others the change was only partial and, on 

 breaking some of these, in the centre was usually found a nucleus 

 or core of coral still retaining its original hardness and composi- 

 tion, while the external parts had been changed from carbonate to 

 phosphate which, though soft and friable, still preserved the 

 structure and appearance of the coral. 



Jarvis' Ma7id.—JsiTYW Island is situated in lat. 0° 22' south 

 and long. 159° 58' west from Greenwich. It is nearly two miles 

 long by one mile wide, trending east and west, and containing 

 about 1000 acres. Like Baker's and Howland's it has the gen- 

 eral features of a coral island, but it differs from them essentia'Jr 

 in the ftict that it once contained a lagoon which has gnidually 

 been filled up with sand and detritus, while the whole island has 

 undergone some elevation. It therefore presents a basin-like 

 form, the surface being depressed from the outer edge towards 

 the centre. It is encircled by a fringing reef, or shore platform, 

 about 300 feet wide; from this a gradually sloping beach re- 

 cedes, the crown of which is from ei^^hteen to twenty -eight feet 

 high, forming a ridge or border, of varying width, which sur- 

 rounds the island like a wall, from the" inshore edge of which 

 the surfiice of the island is gently depressed. 



Within this depression there are other ridges, parallel to the 

 outer one, and old beach lines and water marks, the remaining' 

 traces of the waters of the lagoon, marking its gradual deer. : 

 and final disappearance. 



This flat depressed surface in the centre of the island is ;v 

 seven or eight feet above the level of the sea. It bears but 1 ■ 

 vegetation, consisting of long, coarse grass, mesembryantheinu.- 

 and portulacca, and that is near the outer edges of the islana 

 where the surface is formed of coral sand mixed with more or 

 less guano. In the central and lower parts the surface is cojH' 

 posed of the sulphate of lime, and it is on this foundation that 

 the principal deposit of gnano rests. This feature of Jarvis 

 Island is an important one to consider in studying the difference 

 between the guano found on it and that on Baker's Island, for ij 

 readily explains the presence, in much of the Jarvis Guano, ot 

 the great excess of sulphate of lime, remarked bv all who hnve 

 investigated it, while the unequal mechanical mixture of ' 

 guano with the underlying sulphate accounts for the lack ot 

 formity m different samples. 



In examining the foundation of the guano deposit on Bak 

 or Mowland's Islands, by sinking a shaft verticallv, the J^sr^- 

 conglomerate reef rock is found directly underlyin/the g^^^ 

 Kestmg on this foundation the guano has undergone only such 

 ^t!^^!ft^ -, ^^'""^^^ ^^ produced. On Jarvis' Island, how- 

 ever, after smking through the guano, one first meets wub a 



