THE PROBLEM OF THE METALLIFEROUS VEINS. 197 



canoes in active eruption, and have but disproportionate conceptions 

 of the clouds and clouds of watery vapor which they emit. The 

 enormous volume has, however, been brought home to us in recent 

 3'ears with great force by the outbreak of Mont Pelee, and we of 

 this Acadeni}", thanks to the efforts of our fellow-member, Dr. E. O. 

 Hovey, of the American Museum of Natural History, have had them 

 placed very vividly 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 therefore first present, as 

 fully as the time admits and as fairly as I may, this older view, 

 which still has perhaps the larger 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 evajDorates 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 sec- 

 tion exist, they conduct the water below in relatively large quantity. 

 Shattered or porous rock will do the same, and we know that open- 

 textured sandstones, dipping down from their outcrops and flattening 

 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 investigation, 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 dail}^ 

 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 appre- 

 ciable 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 which we draw. 



The section of the rocks which stands between the surface and the 

 ground water is the arena of active change and is that part of the 

 earth's crust in Avhich the meteoric waters exercise their greatest 

 effect. Rocks within this zone are in constant process of decay and 

 disintegration. Oxidation, involving the production of sulphuric 

 acid from the natural metallic sulphides, is actively in progress. 

 Carbonic acid enters also with the meteoric waters. The rocks are 

 open in texture and favorably 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 downward into the quiet and rela- 

 tively motionless ground water. If the acid solutions escape the pre- 



