Januaby 5, 1906.] 



SCIENCE. 



23 



recognized by all to be the agents for the 

 filling of the veins. 



Let lis now focus attention on the 

 ground-water. This saturates the rocks, 

 fills the crevices and forces the miner who 

 sinks his shaft, to pump, much against his 

 natural inclination. The vast majority of 

 mines are of no great depth, and the nat- 

 ural conclusion of our earlier observers, 

 based on this experience, has been that the 

 ground-waters extend downward, satura- 

 ting the strata of the earth to the limit of 

 possible cavities, distances which vary from 

 1,000 to more than 30,000 feet. To this 

 must be added another familiar phe- 

 nomenon. The interior temperature of the 

 earth increases at a fairly definite ratio of 

 about one degree Fahrenheit for each 60- 

 100 feet of descent. In round numbers, if 

 we start with a place of the climatic condi- 

 tions of New York— that. is, with a mean 

 annual temperature of about 51°, we 

 should on descending 10,000 feet below the 

 surface find a temperature of about 212°, 

 and if we go still deeper, it would be still 

 greater. Of course, under the burden of 

 the overlying column of water, the actual 

 boiling points for the several depths would 

 be greater, and it is a question whether 

 the increase of temperature would over- 

 come the increase of pressure and the con- 

 sequent rise of the boiling point so as to 

 convert this water into steam, cause great 

 increase in its elasticity, decrease in its 

 specific gravity and thereby promote cir- 

 culations. At all events, the rise in tem- 

 perature would cause expansion of the 

 liquid, would disturb equilibrium and to 

 this degree would promote circulations. 



There is one other possible motive power. 

 The meteoric waters enter the rocky strata 

 of the globe at elevated points, sink down- 

 ward, meet the ground-water at altitudes 

 above the neighboring valleys and estab- 

 lish thereby %hat we call head. ' In conse- 

 quence they often yield springs. If we 



imagine the head to be effective to con- 

 siderable depths we have again the deep- 

 seated waters under pressure, which after 

 their long and devious journey through the 

 rocks may cause them to rise eleswhere as 

 springs. The head may in small degree be 

 aided by the expansion of the uprising 

 heated column, whose specific gravity is 

 thereby lowered as compared with the de- 

 scending colder column. 



May we now draw all these facts and 

 supposed or assumed phenomena into one 

 whole 1 



The descending meteoric waters become 

 charged with dissolved earthy and metallic 

 minerals in their downward, their deep- 

 seated lateral and perhaps also at the be- 

 ginning of their heated uprising journey. 

 They are urged on by the head of the 

 longer and colder descending column and 

 by the^ interior heat. They gather together 

 from many smaller channels into larger is- 

 suing trunk channels. They rise from 

 regions of heat and pressure which favor 

 solution, into colder regions of precipitation 

 and erystallizaticn. They deposit in these 

 upper zones their burden of dissolved 

 metallic and earthy minerals and yield 

 thus the veins from which the miner draws 

 his ore. 



This conception is based on phenomena 

 of which the greater part are the results of 

 every-day experience. It is attractive, rea- 

 sonable and is on the whole the one which 

 has been most trusted in the past. Doubt- 

 less it has the widest circle of adherents 

 to-day. It is, however, open to certain 

 grave objections which are gaining slow 

 but certain support. 



The conception of the extent of the 

 ground-water in depth, for example, is 

 flatly opposed to our experience in those 

 hitherto few but yearly increasing deep 

 mines which go below 1,500 or 2,000 feet. 

 Wherever deep 'shafts are located in regidiis 

 other than those of expiring but not clead 



