22 



SCIENCE. 



[N. S. Vol. XXIII. No. 575. 



of the daily life and observation of the 

 great majority of civilized peoples, and for 

 this reason they have not received the at- 

 tention that otherwise would have fallen 

 to their share. Relatively few geologists 

 have the opportunity to view volcanoes in 

 active eruption, and have but dispropor- 

 tionate conceptions of the clouds and clouds 

 of watery vapor which they emit. The 

 enormous volume has, however, been 

 brought home to us in recent years, with 

 great force, by the outbreak of Mont Pelee, 

 and we of this academy, thanks to the 

 efforts of our fellow-member. Dr. E. 0. 

 Hovey, of the American Museum of Nat- 

 ural History, have had them placed very 

 vividlj'' before us. It is on the whole not 

 surprising that to the meteoric waters most 

 observers in the past have turned for the 

 chief, if not the only, agent. I will, there- 

 fore, first present as fully as the time ad- 

 mits, and as fairly as I may, this older view 

 which still has perhaps the largest number 

 of adherents. 



Except in the arid districts, rain falls 

 more or less copiously upon the surface of 

 the earth. The largest portion of it runs 

 off in the rivers; the smallest portion 

 evaporates while on the surface, and the 

 intermediate part sinks into the ground, 

 urged on by gravity, and joins the ground- 

 waters. Where crevices of considerable 

 cross-section exist, they conduct the water 

 below in relatively large quantity. Shat- 

 tered or porous rock will do the same and 

 we know that open-textured sandstones 

 dipping down from their outcrops and flat- 

 tening in depth lead water to artesian 

 reservoirs in vast quantity. As passages 

 and crevices grow smaller, the friction on 

 the walls increases and the water moves 

 with greater and greater difficulty. When 

 the passage grows very small, movement 

 practically ceases. The flow of water 

 through pipes is a very old matter of in- 

 vestigation, and all engineers who deal with 



problems of water supply for cities or with 

 the circulation of water for any of its 

 countless applications in daily life must be 

 familiar with its laws. Friction is such 

 an important factor that only by the larger 

 natural crevices can the meteoric waters 

 move downward in any important quantity 

 or with appreciable velocity. They do sink, 

 of course, and come to comparative rest 

 at greater or less distance from the surface 

 and yield the supplies of underground 

 water upon Avhich we draw. 



The section of the rocks which stands 

 between the surface and the groundwater 

 is the arena of active change and' is that 

 part of the earth's crust in which the 

 meteoric waters exercise their greatest 

 effect. Rocks within this zone are in con- 

 stant process of decay and disintegration. 

 Oxidation, involving the production of sul- 

 phuric acid from the natural metallic sul- 

 phides, is- actively in progress. Carbonic 

 acid enters also with the meteoric waters. 

 The rocks are open in texture and favor- 

 ably situated for maximum change. From 

 this zone we can well imagine that all the 

 finely divided metallic particles which are 

 widely and sparsely distributed in the rocks 

 go into solution and tend to migrate down- 

 ward into the quiet and relatively motion- 

 less ground-water. If the acid solutions 

 escape the precipitating action of some 

 alkaline reagent such as limestone they 

 may even reach the ground-waters, ajid 

 their dissolved burdens may be contributed 

 to this reservoir, but the greater portion 

 seems to be deposited at the level of the 

 ground-water itself or at moderate dis- 

 tances below it. Impressed by these phe- 

 nomena which present a true cause of solu- 

 tion, and influenced by their familiar and 

 every-day character, we may build up on 

 the basis of them a general conception of 

 the source of the metallic minerals dis- 

 solved in those aqueous solutions which are 



