1S90.] XEW YORK ACADEMY OF SCIENCES. 85 



to point; the local press is wildly excited; and the native 

 *' cracker '^ occupants are suddenly aroused by a rise of value in 

 their barren little holdings, that turns their heads with un- 

 dr(amed-of wealth. One poor man, at least, has become ac 

 tually insane at realizing $300 for an option on his land, when 

 probably he had never before seen such a thing as a twenty- 

 dollar note. 



As regards phosphate deposits in general, we may first glance 

 at the two extremes of their occurrence. In the oldest rocks of 

 the continent. — the Archaean of Canada, — we have the crystalline 

 phosphate of lime (apatite) in large amount; while at the pres- 

 ent time there are still forming extensive deposits of bird-manure 

 (guano) on many islands like the Chinchas, etc. Between these 

 extremes of age and of condition, there is every possible inter- 

 mediate grade. On rocky islands like those off the arid coast of 

 Peru, where rain is slight and rare, only fermentation occurs, 

 and the phosphoric acid is largely soluble and combined me- 

 chanically with organic salts, as urates and oxalates. But when 

 formed within the rain-belt, and constantly subject to its influ- 

 ence, the soluble compounds, including ammonia and phosphoric 

 acid, are leached out. When this has occurred on limestone or 

 coral islands, a third type of material is produced by the action 

 of these leached-out compounds on the carbonate of lime, alter- 

 ing it to phosphate, as on Aruba and Sombrero. If there is 

 much iron or alumina present, the less desirable phosphates of 

 those bases may be similarly formed. 



As to the rate at which bird-guano is accumulated, — which is 

 the main source of the tropical phosphate-beds of recent geolo- 

 gical time, — the following very definite evidence is of interest. I 

 was personally acquainted with an intelligent captain who was 

 sent to a coral island in the South Pacific for a cargo of guano. 

 The island was uninhabited, and the birds were there in count- 

 less swarms. The same captain had been there twenty years 

 before; and the place hud been unvisited since that time. On 

 this former ti-ip, his men had built a hut of coral rock, after 

 clearing off a space for it, and covered it with a piece of sail, as 

 a shelter during their stay. On leaving, they took away the sail 

 and left the "hypsthral" hut with its board flooring. On 

 returning after twenty years, the fresh deposit had accumulated 

 within the hut to a depth of twenty inches, — showing a rate of 

 about one inch per annum, — while the underlying coral lime- 

 stone was altered to phosphate for several feet, gradually passing 

 into carbonate in going down. 



At some points, especially in caverns (as e.g. in Cuba) bat- 

 guano accumulates to a degree sufficient to become valuable in 

 commerce. This material is easily recognized by containing 



