64 THE PROBABLE SEAT OF VOLCANIC ACTION. *VL] 



integration, and for the chemical action of the acids, which, as 

 shown in the two papers just referred to, must have been pres- 

 ent in the air and the waters of the time. It is, moreover, not 

 improbable that a yet unsolidified sheet of molten matter may 

 then have existed beneath the earth's crust, and may have in- 

 tervened in the volcanic phenomena of that early period, con- 

 tributing, by its extravasation, to swell the vast amount of 

 mineral matter then brought within aqueous and atmospheric 

 influences. The earth, air, and water thus made to react upon 

 each other, constitute the first matter from which, by mechan- 

 ical and chemical transformations, the whole mineral world 

 known to us has been produced. 



It is the lower portions of this great disintegrated and water- 

 impregnated mass which form, according to the present hypoth- 

 esis, the semi-liquid layer supposed to intervene between the 

 outer solid crust and the inner solid and anhydrous nucleus. 

 In order to obtain a correct notion of the condition of this mass, 

 both in earlier and later times, two points must be especially 

 considered, the relation of temperature to depth, and that of 

 solubility to pressure. It being conceded that the increase 

 of temperature in descending in the earth's crust is due to the 

 transmission and escape of heat from the interior, Mr. Hopkins 

 showed mathematically that there exists a constant proportion 

 between the effect of internal heat at the surface and the rate at 

 which the temperature increases in descending. Thus, at the 

 present time, while the mean temperature at the earth's surface 

 is augmented only about one twentieth of a degree Fahrenheit, 

 by the escape of heat from below, the increase is found to be 

 equal to about one degree for each sixty feet in depth. If, 

 however, we go back to a period in the history of our globe 

 when the heat passing upwards through its crust was sufficient 

 to raise the superficial temperature twenty times as much as at 

 present, that is to say, one degree of Fahrenheit, the augmen- 

 tation of heat in descending would be twenty times as great 

 as now, or one degree for each three feet in depth. (Geol. Jour- 

 nal, VIII. 59.) The conclusion is inevitable that a condition 

 of tilings must have existed during long periods in the history 



