1884.] 197 [Wadsworth. 



Mr. F. W. Putnam occupied the rest of the evening with an in- 

 teresting account of discoveries by Dr. Metz and himself in 

 mounds of the Little Miami Valley. He also showed a portion 

 of a human jaw-bone discovered by Dr. Abbott in the Trenton 

 gravel ; and human footprints in tufa in Nicaragua found sixteen 

 feet from the surface under several strata of tufa and sands by 

 Dr. Earl Flint. 



The following papers were read by title : 



THE THEORIES OF ORE DEPOSITS. 



BY M. E. WADSWORTH. 



The recent publication of the interesting chapter of Professor 

 Sandberger's work relating to mineral veins, in the Engineering 

 and Mining Journal- (Vol. xxxvn, pp. 186, 198, 218, 219, 232, 

 233) has served to call renewed attention, on the part of Ameri- 

 can mining men, to the theories of ore deposits. The theory of 

 lateral secretion (infiltration, segregation, and impregnation) so 

 strongly advocated by Sandberger is very old, and has been a fa- 

 vorite one among American writers on the subject of mineral 

 veins, appearing even in the older text books, like Whitney's Me- 

 tallic Wealth of the United States, 1854, pp. 62-68, and Dana's 

 Manual of Geology, 1863, pp. 712-714. This theory appears to 

 have a direct connection with many other forms of ore de- 

 posits, besides true fissure veins, and to follow from a universal 

 law, intimately interwoven with the history of the rocks 

 of this globe. It is proposed here to point out this law and its 

 relation to ore deposits, and to call attention to the uncertainty 

 of conclusions drawn from the analysis of the wall rock and its 

 contained minerals. In order to do this, it is necessary to pre- 

 sent a brief but comprehensive view of the entire field. 



Without entering at all upon the question of the source of those 

 rocks which have come from below the earth's surface, which are 

 known as eruptives, and which form a large portion of the 

 so-called metamorphic series, it is sufficient for the present pur- 

 pose to state that when they reach the exterior of the earth, their 

 condition is one not adapted to the circumstances in which they 



