NEW YORK ACADEMY OF SCIENCES 649 



the very foundation from beneath the conception of the meteoric 

 waters and tumbles the whole structure in a heap of ruins. 



While I would not wish to positively make so sweeping a 

 statement as this about a question involving so many uncer- 

 tainties, there is nevertheless a growing conviction among a 

 not inconsiderable group of geologists that the rocky crust of 

 the earth is much tighter and less open to the passage of descend- 

 ing waters than has been generally believed; and that the 

 phenomena of springs, which have so much influenced conclu- 

 sions in the past, affect only a comparatively shallow, overlying 

 section. Such phenomena of cementation as we see are probably 

 in large part due to the action of water stored up by the sedi- 

 ments when originally deposited and carried down by them 

 with burial. Under pressure a relatively small amount of water 

 may be an important vehicle for recrystallization. 



It has been assumed in the above presentation of the case 

 of the meteoric waters that they are able to leach out of the 

 deep-seated wall-rocks the finely disseminated particles of 

 the metallic minerals, but the conviction has been growing in 

 my own mind that we have been inclined to overrate the prob- 

 ability of this action in our discussions. In the first place 

 our knowledge of the presence of the metals in the rocks them- 

 selves is based upon the assay of samples almost always gathered 

 from exposures in mining districts. The rock has been sought 

 in as fresh and unaltered a condition as possible, and endeavors 

 have been made to guard against the possible introduction of 

 the metallic contents by those same waters which have filled 

 the neighboring veins. But if we admit or assume that the 

 assay values are original in the rock, and, in case the, latter is 

 igneous, if we believe that the metallic minerals have crystal- 

 lized out with the other bases from the molten magma, we are 

 yet confronted with the fact that their very presence and detec- 

 tion in the rock shows that they have escaped leaching even 

 though they occur in a district where underground circulations 

 have been especially active. From the results which we have 

 in hand it is quite as justifiable to argue that the metals in 

 the rocks are proof against the leaching action of underground 

 circulations as that they fall victims to it. These considera- 



