188 W. J. Taylor on Rock Guano. 



points whicli were distinctly crystals of vivianite. The bones 

 were in a perfect state of preservation, and afforded, "when 

 treated with hydrochloric acid, a skeleton of gelatine, proving 

 that gelatine does not resist the absorption of the ferruginous 



compound. 



Various theories have been formed and published as to the 

 origin of the rock guano; these are most likely premature, as 

 the accounts as to its occurrence are founded on rej)orts of those 

 not accustomed to noting geological phenomena. 



The islands of the Caribbean Sea are very varied. Some are 

 quite low and covered with sand composed of fragments of 

 siiells, madrepore and corals, which can readily be distinguished 

 with a pocket lens. These sands are resorted to by myriads of 

 waterfowls for laying their eggs. One of the captains who vis- 

 ited there mentions that it is necessary to make one's way 

 through them with a stick. Other islands attain heights of 800 

 feet ; it seems improbable that such heights could be created by 

 accretions of guano and sand, when the islands were subject to 

 ^ continued action of the waves of the ocean ; and from the 

 •inclined position of the guano layers it might be inferred that 

 »n uplift had taken place since the layers were formed. But on 

 this point more direct evidence is needed. 



It is most probable that the guano rock from some of the 

 islands has been changed in its composition by reactions of the 

 salts contained in sea water; but before such reactions can be 

 fully explained, accurate analyses must be made of this sea 



water. 



It is a remarkable fact, that the composition of the ash from 

 the recent guano from the heights of tne Centinella rock com- 

 posed of phosphates of alumina and iron, should have a compo- 

 sition so very near that of the guano rock from the Los Monges 

 and El Roque islands. The frequent occurrence of alumina and 

 iron is to be remarked in the guano rocks. 



Note, — ^I have just been informed by Dr. Luther, that from 

 analyses lately made in Baltimore of a cargo of rock guano that 

 has lately arrived from the island of Testigoes, there has been 

 foimd from forty to forty -five per cent of phosphoric acid. 



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