C. H. HITCHCOCK — THE REDONDA PHOSPHATE. 9 



below as a phosphuret , which has since changed its character through oxidation and 

 hydration ? 



The discovery of this mineral in a volcanic rock recalls the presence of apatite in 

 Archean granites, Paleozoic diabases and other massive rocks, which are assuredly 

 of igneous origin. Our studies into the soils of New Hampshire led us to refer the 

 origin of the small percentage of phosphorus found in them to the decay of the under- 

 lying granites carrying microscopic crystals of apatite rather than to any organisms of 

 modern times. ■^ If phosphates may occur in the ancient crystallines as original min- 

 erals, it is reasonable to believe that similar compounds might be found in recent 

 lavas. 



The dealers in fertilizers will be pleased if we can refer them to any new source of 

 phosphates. Hitherto no one has thought of searching for phosphates in volcanic rocks. 

 As they so greatl}'' resemble decayed rocks or ferruginous earths, observers may have 

 overlooked them in volcanic regions. With attention now directed to the possibilit}' 

 of finding phosphates in lava, future explorers may make important discoveries in 

 regions now regarded as valueless for economic purposes. 



Professor N. H. Winchell : I should like to inquire of Professor Hitchcock if 

 there is any objection known to him to considering this peculiar phosphatic deposit 

 the result of leaching from ordinary phosphate or guano. I understood him to de- 

 scribe the substance as embracing masses, large and small, of the rock of the island, 

 in a manner similar to that in which mortar embraces stones in a stone wall, and that 

 much of the island is composed, at least superficially, of loose rocks thus cemented 

 together. Those volcanic islands may date back to Tertiary or Cretaceous times. 

 They naturally would always have been the roosting and breeding places for aquatic 

 or other fowls. At the same time the region of volcanic activity is one of copious 

 rains — rains that are often saturated with acids that characterize volcanic regions. 

 Such acid waters would act powerfully on the native guano, and would dissolve and 

 remove any lime that it contained. The residue would be carried downward and 

 deposited by the drainage among the loose stones that composed the mountain side, 

 and would even permeate the scoriae and insinuate itself between successive lava flows. 

 On analysis it would be found to resemble that which Professor Hitchcock has pre- 

 sented. 



Professor Hitchcock: The phosphate is not found in the loose stones or tufa de- 

 posits, but in close connection with solid basaltic lava. The so-called stones are prop- 

 erly examples of the columnar structure so common in lava, but the concentric masses 

 are spherical rather than cylindrical in shape, and the enclosed minerals do not bear 

 more marks of infiltration than do the feldspar crystals of porphyry or the chrysolite 

 in basalt. Guano would have been too limited in amount to have equalled the many 

 thousand tons of the visible phosphate. Mr. P. T. Cleve, of Sweden, describes the 

 lava of the Windward islands, including Redonda, as of Quaternary age, and the 

 fires have hardly died out yet. 



Further remarks on the communication were made by E. W. Claypole 

 and A. S. Tiffany. 



* Geology of New Hampshire, Part IV, 1878, p. 94. 



II— Bull. Geol. Soc. Am., Vol. 2, 1890. 



