THE PROBLEM OF THE METALLIFEROUS VEINS. 203 



two-himdred-and-thirty-seventh as the result. That is, if we take a 

 cubic inch of granite and thoroughly dry it, it will absorb water up to 

 one two-hundred-and-thirtj'^-seventh of its weight. The volume of 

 this water indicates the open spaces or voids in the stone. The aver- 

 age of the specific gravities of the 33 granites is 2.G47. If by the 

 aid of this value we turn our weight of water into volume, we find 

 that its volume is one-ninetieth that of the rock. For the four dia- 

 bases and gabbros, similarly treated, the ratio of absorption is one 

 three-hundred-and-tenth ; the specific gravity is 2.776 and the ratio 

 of volume one one-hundred-and-tenth. We can express all this 

 more intelligibly by saying that if we assume a cube of granite and 

 if we combine all its cavities into one crack passing through it, par- 

 allel to one of its sides, the width of the crack will be to the edge of 

 the cube, as 1 to 90. In the diabases and gabbros, similarly treated, 

 the ratio will be 1 to 110. These values are very nearly the same as 

 the average of the ratios of the edges of the cubes of rock and ore 

 given in the table on page 202, it being 1 to 104. We may conclude, 

 therefore, that in so far as we can check the j)revious conclusion by 

 experimental data it is not far from the truth. 



It may be stated that the porphyritic igneous rocks which have 

 furnished nearly all the samples for the above analyses are as a rule 

 extremely dense, and that their absorptive capacity is more nearly 

 that of the compact granites than the open-textured ones. It is 

 highh^ improbable that underground water circulates through these 

 rocks to any appreciable degree except along cracks which have been 

 produced in the mechanical way, either by contraction in cooling 

 and crystallizing or by faulting and earth movements. The cracks 

 from faulting are very limited in extent, and in the greater number 

 of our mining districts they affect but narrow belts, small fractions 

 of the total. Of the cracks from cooling and crystallizing those of 

 us who have seen rock faces in crosscuts and drifts underground 

 Avhere excavations have been driven away from the veins proper can 

 form some idea if we eliminate the shattering due to blasting. My 

 own impression is that in rocks a thousand feet or so below the sur- 

 face such cracks are rather widely spaced, and that when checked in 

 a general way by the ratios just given these rocks are decidedly 

 unfavorable materials from which the slowly moving meteoric ground 

 waters (if such exist) may extract such limited and finely distributed 

 contents of the metals. 



I have also endeavored to check the conclusions by the recorded 

 experience in cyaniding gold ores in which fine crushing is so impor- 

 tant, and I can not resist the conviction that we have been inclined 

 to believe the leaching of compact and subterranean masses of rock a 

 much easier and more probable process than the attainable data 

 warrant. 



