Fernando d< Noronha. 255 



e mean tide. The encroachment of the son has re- 

 moved the supporting igneous rocks, and great fragments, 

 some of them over fifty feet across and twenty feet in i hick- 

 no.'-, have slid down t<> the beach. This ledge and its fallen 

 fragments are Bhown in fig. 7. Where these rocks abut against 

 the hill, they have a steep dip toward the island, suggesting 

 that the bedding was produced by sand having been blown 

 over the top of a dime. 



Of the ancient sands but few unconsolidated remnants are 

 now to he found upon these islands. On the top of the ridge 

 at the extreme northeast point of the island is some not hard- 

 ened into solid rock. This sand like that of all the present 

 beaches about the island has a clearly marked sonorous prop- 

 erty, crunching and creaking beneath the feet like dry snow. 



In 1881 the Brazilian Minister of Agriculture sent a commis- 

 <i"ii to Fernando de Xoronha to examine and report upon the 

 phosphate of lime found on Ilha Rapta: This phosphate of 

 lime overlies the a^olian sandstone of that island, and Mr. 

 Derby say- in his report* that it is probably the insoluble res- 

 idue from a deposit of guano, the parts soluble in water having 

 been washed out by rains. Mr. Derby's explanation is no 

 doubt the correct one. It may be added, however, that this 

 phosphate occurs over the etched surface of the calcareous 

 rock, and this rock has doubtless added to the total amount of 

 phosphate of lime on the island for this amount would be 

 materially increased by the presence of the calcareous rock 

 underlying the deposit. The rainwater would dissolve from 

 the guano the soluble phosphates of lime and ammonia and 

 these, upon coming in contact with the carbonate of lime be- 

 neath, would form insoluble pnosphate of lime and soluble 

 carbonate of ammonia, the latter being carried off. 



The writer observed several illustrations of the formation of 

 solid rock-like masses of the insoluble phosphate of lime in 

 what seem to have been crevices or porous vertical streaks in the 

 calcareous rock. Of the following analyses, No. 1 is of this hard 

 phosphatic rock broken from the indurated seolian sandstone. 



It is noteworthy that typical specimens of these seolian sand- 

 stones, whether very porous or compact, and whether from Ilha 

 Rapta or elsewhere, show upon analyses the presence of some 

 phosphate of lime. Analysis 2, beyond, is of the average clean 

 and compact part of the Ilha Rapta seolian sandstone. The 

 piece w as broken from one of the tall jagged points left by the 

 etching out of the surface by the combined action of rain water 

 and ocean spray. 



*My copy of this report has for title simply "0 Phosphato de Cal; " it bears 

 neither place nor date of publication, but it was probably published by the Bra- 

 zilian government in 1881 at Rio de Janeiro. 



