440 REPORT OF NATIONAL MUSEUM, 1904. 



deposits from aqueous solution which took place either in depressions 

 of the surface or in vertical fissures of the nature of gash veins pro- 

 duced by the shrinkage of the calcareous strata." 



These views differed from the more modern in that it is now deemed 

 as. probable that the ores were first precipitated in an ocean in which 

 they were held in solution as sulphates and reduced to sulphides 

 through the decomposing organic matter; that subsequently, through 

 the action of percolating surface waters, the same were once more 

 oxidized, segregated in the fissures, and reduced a second time to the 

 condition of sulphides. The production of the mines in the Missis- 

 sippi Valley he regarded as having even then reached its maximum. 



Whitney recognized the eruptive nature of the Iron Mountain 

 masses of Missouri, and apparently regarded the hematite ores of the 

 Lake Superior region as also of an eruptive nature (see also p. 417), 

 though the later work of Van Hise has shown them to have had a 

 chemical origin. Concerning the specular and magnetic iron ores of 

 New York, he thought to have found the evidence of direct eruptive 

 origin as perhaps less conspicuous, many exhibiting appearances of 

 secondary action, such as might have been brought about by volcanic 

 agencies and powerful currents which swept awa} T and abraded por- 

 tions of the original eruptive masses, "rearranging their particles and 

 depositing them again in the depressions of the strata." The lenticu- 

 lar beds of ore occurring parallel with the stratification were particu- 

 larly referred to as originating in this way. 



A year later (November, 1855) Whitney had in the American Jour- 

 nal of Science an article on the changes which take place in the struc- 

 ture and composition of mineral veins, which is of interest in connec- 

 tion with the recent revival of the subject of secondary enrichment of 

 ore deposits. He here described the now well-known copper deposits 

 of Ducktown, Tennessee, and the superficial alteration of the vein 

 matter, and called attention to the fact that the black ore, then being 

 mined, was formed by a process of natural concentration by surface 

 water, which was constantly decomposing the material above the per- 

 manent water level and carrying it downward to the point where it 

 was stopped by the solid portion of the vein. By this means a large 

 portion of the copper once disseminated throughout perhaps 100 feet 

 of A^ein stone 'had become concentrated into a thickness of perhaps 2 

 or 3 feet. 



In June, 1854, Lewis Harper, or properly, Ludwig Hafner, was 

 elected by the trustees to the chair of geology in the University of 



«Dr. Henry King, in a sketch of the geology of the Mississippi Valley, read before 

 the Association of American Geologists and Naturalists in 1844, and printed in the 

 American Journal of Science for that year, argued that the ores of zinc, copper, and 

 lead occurring in the Cliff limestone were deposited contemporaneously with the 

 inclosing rock. 



