/ D. Hague on the Guano Islands of the Pacific Ocean. 23 1 



3 compact and crystalline, 



tlj two feet 



3 successive strata of coraf sand and shells 



s) frequently two feet thick, beneath 

 " ;oral s ' ^ ■ " - 



. the gradual process by which the 



positea one 

 lagoon was 



uiieu up." 



Of the origin of this sulphate of lime there can hardly be any 

 doubt. As the lagoon was nearly filled up, while, by the grad- 

 ual elevation of the island, the communication between the outer 

 ocean and the inner lake was constantly becoming less easy, 

 ust have been evaporated in the 



large quantities of 5 

 basin. By this m< 



deposits would be formed containing 

 common salt, gypsum and other salts found in the waters of the 

 ocean. From these the more soluble parts would gradually be 

 washed out again by the occasional rains, leaving the less solu- 

 ble^sulphate of lime as we find it here. 



Some additional light is thrown on this matter by the different 

 parts of the surface, which, though nearly flat, shows some slight 

 variety of level. The higher parts, particularly around the outer 

 edges, are composed chiefly of coral sand, either mixed with or 

 underlying guano. Nearer the centre is a large tract, rather 

 ^•^re depressed, forming a shallow basin in which the bulk of 

 the sea water must have been evaporated, and whose surface 

 (now partly covered with guano) is a bed of sulphate of lime, 

 ^^hile, further, there is a still lower point, the least elevated of 

 Ae whole, where the lagoon waters were, without doubt, most 

 yecently concentrated. This latter locality is a crescent shaped 

 bed, about 600 feet long by 200 or 300 feet wide, having a sur- 

 face very slightly depressed from the outer edge towards the 

 niiddle. Around the borders are incrustations of crystallized 

 gypsum and common salt, ripple marks and similar evidences of 

 toe gradually disappearing lake. The whole is composed of a 

 crystalline deposit of sulphate of lime, which, around the borders, 

 J5 already observed, is mixed with some common salt, while near 

 the centre, where rain water sometimes collects after a heavy 

 SQower, the salt is almost entirely washed out, leavmg the gyp- 

 ^•im by itself. It is closely, but not hard, packed, and is still 

 ^ery wet By diaainff 18 or 24 inches down, salt water may 

 generally be found! ^. . . 



These facts help us to understand the varying conditions m 

 ^hich we now find the guano beds, since the most important 

 f '■t, and that from which the importations have thus far come, 

 f^\3 on a bed of sulphate of lime, of an earlier but similar origm 

 ;V.^at just described above: a part rests on a coral formation, 

 ^^'le still another part, covering a large tract, has been by the 



