NEW YORK ACADEMY OF SCIENCES 647 



overcome the increase of pressure and the consequent 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 circulations. At all events, 

 the rise in temperature 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 downward, meet the ground-water at altitudes above the 

 neighboring valleys, and establish thereby what we call head. 

 In consequence they often yield springs. If we imagine the 

 head to be effective to considerable 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 

 elsewhere 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 descending 

 colder column. 



May we now draw all these facts and supposed or assumed 

 phenomena into one whole? 



The descending meteoric waters become charged with dis- 

 solved earthy and metallic minerals in their downward, their 

 deep-seated lateral, and perhaps also at the beginning 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 issuing trunk channels. They rise from regions 

 of heat and pressure which favor solution, into colder regions 

 of precipitation and crystallization. They deposit in these 

 upper zones their burden of dissolved metallic and earthy miner- 

 als 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 everyday experience. It is attractive, 

 reasonable, and is on the whole the one which has been most 

 trusted in the past. Doubtless it has the widest circle of adher- 

 ents to-day. It is, however, open to certain grai^e objections 

 which are gaining slow but certain support. 



