NOVEMBEE 15, 1901.] 



SCIENCE. 



749 



to 100 feet, one fourteen-hundredth of 

 one per cent, of the metals in the rocks 

 could supply all the lead and zinc which 

 has been or is likely to be taken from the 

 district. It is therefore not necessary to 

 suppose that there is more than a minute 

 quantity of metallic material in the zone of 

 fracture, to furnish a supply adequate many 

 times over to account for all the deposits 

 which have been mined or are likely to be 

 mined. 



So far as the specific work of under- 

 ground water is concerned, we have al- 

 ready seen that the metals for the ores are 

 derived from the zone of fracture. But it 

 does not follow that important supplies of 

 metals to be later yielded to the water may 

 not come from deeper within the earth. 

 As a result of various causes, which can- 

 not be discussed this evening, the igneous 

 rocks rise from an unknown depth below 

 the surface of the earth into the zone of 

 fracture or even quite to the surface. Such 

 igneous rocks bear materials out of which 

 many important ore deposits are largely 

 or wholly derived. Indeed, if we go far 

 enough back in the history of the earth, 

 all rocks were probably derived from the 

 igneous rocks. So, directly or indirectly, 

 the ultimate source from which ores are 

 derived by underground water is igneous 

 rocks, either ancient or modern. On 

 this point there are no differences of opin- 

 ion. 



But there are differences of opinion as to 

 the manner in which the ores are derived 

 from the igneous rocks. Some geologists 

 hold that the direct processes of igneous 

 action produce many ores. They say that 

 during the process of crystallization of the 

 igneous rocks the ores are segregated by 

 magmaticorpneumatolitic processes. There 

 are cases in which this is probably true, as, 

 for instance, the unimportant titaniferous 

 iron ores of the Adirondacks and the Lake 

 Superior region. Certain ores, as the tin 



ores, possibly have this origin. But it is yet 

 unproved that the great mass of ores, which 

 are known as the oxidized ores, the carbo- 

 nate ores, the sulphide ores, and the tel- 

 lurid ores, have been thus derived. "We 

 know of these classes of ores that a large 

 part have been taken from the rocks and 

 brought to their present positions by un- 

 derground water. Why, then, assume some 

 other process of segregation for which 

 there is no adequate evidence, when we have 

 a wholly adequate agent in underground 

 water? In the great majority of cases the 

 ores are taken from the igneous, sedimen- 

 tary and metamorphic rocks by the under- 

 ground waters ; are carried to their present 

 positions by the underground waters, 

 and deposited by the underground waters 

 at the places where they are now ex- 

 ploited. 



The next question which naturally arises 

 is the source of the underground water. 

 It is believed that the water is predomi- 

 nantly of meteoric origin ; in other words, 

 is the water which falls from the atmos- 

 phere upon the valleys and hills and moun- 

 tains of Colorado and other parts of the 

 world. It is true that each igneous rock 

 usually carries a small amount of water ; 

 and in the aggregate this amount may be 

 very great. Indeed, it may be that all the 

 water upon the surface of the earth and 

 that in the openings of the zone of fracture 

 was originally derived from the igneous 

 rocks. But even if this be true, it does not 

 follow that in a given district, at the partic- 

 ular epoch in which the ore deposits were 

 formed, the water directly derived from 

 the igneous rocks is adequate or even im- 

 portant in accounting for this deposition. 

 As already explained, it is necessary to 

 consider not only the ore but the gangue 

 material with which it is related ; and it 

 has been seen that in order to deposit an 

 ore and its accompanying gangue probably 

 required tens of thousands or even hun- 



