748 



SCIENCE. 



[N. S. Vol. XIV. No. 359. 



the center of the earth. And it must be 

 remembered that all rocks are limited in 

 strength. The strongest rock tested has a 

 crushing strength of something more than 

 40,000 pounds per square inch. A column 

 of such a rock 10 or 12 miles high would 

 be crushed hy its own weight. It is easily 

 calculable that if we suppose the outer part 

 of the crust of the earth to be composed 

 only of the strongest rocks, and we imagine 

 openings to exist in these rocks, then at a 

 certain depth these cracks must be closed 

 by the pressure. And this deduction has 

 been experimentally proved. Professor 

 Adams, of Montreal, has shown that rocks 

 subjected to pressures in all directions 

 greater than their crushing strength may 

 be mashed, and no perceptible openings 

 produced. Therefore, openings of great size 

 cannot be assumed to exist below a very 

 limited depth in the crust of the earth. 

 This conclusion is fully verified by obser- 

 vation. By examining the rocks in the 

 cores of mountain ranges where there has 

 been deep denudation, we may see what 

 has happened to them when well below the 

 surface. In the Front Range of Colorado, 

 and at various places in the world, where 

 the rocks have been deformed at consider- 

 able depth below the surface of the earth 

 (ignoring recent fractures which have been 

 produced since the rocks came near or to the 

 surface), the process has taken place with- 

 out the formation of openings larger than 

 those discernible only with the microscope. 

 Therefore, from the point of view of pure 

 physics, from the point of view of experi- 

 ment, and from the point of view of observa- 

 tion alike, we reach the conclusion that no 

 large or continuous cracks or crevices exist 

 except for a very limited depth below the 

 surface of the earth. 



In order to deposit the metals and gangue 

 of an ore deposit, a vigorous circulation 

 is required. The vigorous circulation of 

 underground water is necessarily confined 



to that part Of the crust of the earth where 

 there are continuous cracks and crevices of 

 considerable size. As the openings decrease 

 in size, the resistance due to friction in- 

 creases rapidly ; and where the openings 

 are subcapillary, it is enormous, being in 

 fact sufficient to practically check circula- 

 tion. In Colorado a common gangue mate- 

 rial is quartz. Springs have been analyzed, 

 and it has been found that the water issuing 

 from such springs bears perhaps one part in 

 one hundred thousand, or one part in a 

 million, of silica. It is probably rather 

 uncommon for a solution to deposit as much 

 as one part by weight in one hundred thou- 

 sand of the gangue and ore material. If 

 this be so and the gangue be quartz, in 

 order to fill an opening with ore and gangue, 

 at least 260,000 times as much water must 

 have passed through it. 



It therefore follows that if the majority of 

 ore deposits are placed where they are by 

 underground waters — and from this there 

 seems no escape — the processes of their 

 gathering and deposition must be mainly 

 confined to the outer few miles of the crust 

 of the earth. This is called the zone of 

 fracture. Therefore my second fundamental 

 conclusion is that the ore deposits are derived 

 from the zone of fracture. 



But is there an adequate source of supply 

 of metallic material in the outer part of the 

 crust of the earth? In answer to this 

 question, it may be said that calculation 

 clearly shows the relatively small quantities 

 of ore which exist could have been derived 

 from the zone of fracture, even if the rocks 

 contain an exceedingly small fraction of one 

 per cent, of metal. To illustrate, Mr. Buell 

 has calculated for Professor Chamberlin, for 

 the Wisconsin lead and zinc district, that if 

 the richest portion of the district be taken, 

 and it be assumed that the supply extended 

 only one- half as far beyond the deposits as 

 the radius of the productive area, and the 

 depth of vertical distribution be confined 



