Trans. N. V. Ac. Set. 6 Oct. i6, 



waves. If in fact no dykes nor fissures existed, such tunnel-like cham- 

 bers could hardly have been perforated by natural causes, for they are 

 on various sides of the island, in various kinds of rocks, and the debris 

 is entirely cleared away. If the caves had been produced by causes 

 now in action, the fallen blocks would remain. The material of the 

 blocks is tough and not liable to disintegration ; nevertheless it has 

 been thoroughly cleared out. as though by the hand of man ; no shin- 

 gle being found on the shore. It is important to notice that the ap- 

 proaches to the caves are over low, flat ground, furrowed by canals 

 leading up to their entrances, /. e., as if artificially excavated for the 

 entrance. 



October i6, 1882. 



SECTION OF GEOLOGY. 



The President, Dr. J. S. Newberry, in the Chair. 



Twenty-four persons present. 



A paper was read by Dr. Alexis A. Julien, on 



THE GENESIS OF THE CRYSTALLINE IRON ORES. 



(Abstract.) 

 Theories of two classes have been advanced, referring the origin of 

 the crystalline ores to extraneous and indigenous origin. Under the 

 first class, three may be mentioned : 



1. Meteoric fall. — This was suggested in reference to the huge 

 hematite deposit of Cerro de Mercado, in Mexico. 



2. Eruption as dykes. — A theory advanced to account for many 

 foreign deposits, and also those of Huronian age in the vicinity of 

 Lake Superior, etc. 



3. Sublimation into fissures. — A theory founded on the observation 

 of crusts of specular oxide of iron in the lavas of Vesuvius, etc. 



Objections to these theories were briefly presented. The theories at- 

 tributing the origin of crystalline ores to indigenous origin are of two' 

 kinds, chemical and mechanical. Several chemical theories have been 

 proposed : 



4. Concentration from ferriferous rocks, or lean ores : if silicious, by 

 thermal solutions : if calcareous, by carbonated waters. Subaerial 

 processes of this kind cannot account for the origin of submarine sedi- 

 ments, such as the crystalline iron ores. 



5. Saturation of porous strata by infiltrating ferriferous solutions. — 

 Such a process could not produce huge bodies of pure ore, nor the 

 alternation of pure materials in the lean laminated ores. 



6. Infiltration into subterranean chambers. — The form, lamination. 



