Xlvi PEOCEEDINGS OF THE GEOLOGICAL SOCIETY. 



heat, and still preserving its " chaleur d'origine " under the cnist of 

 rocks which has cooled and crystallized to some depth from the sur- 

 face, and the sheets of earthy sediment deposited beneath the waters 

 which that cooling allowed to be collected ? Is this fundamental 

 assumption true ? and, if true, are these consequences fairly derivable 

 from it ? Is the globe passing through a series of conditions which 

 never can be repeated, a series having a clear trace of a beginning, a 

 sure prospect of an end ? 



Towards the settling of these questions geology contributes some- 

 what, physical research something more. The earth is hot within ; 

 this heat flows to the surface in a feeble stream, and augments the 

 temperature there by a small fraction of a degree. The temperature 

 at the surface is thus constituted by radiation from the sun and 

 heavenly bodies, added to that received by conduction and convection 

 from the interior of the earth, and diminished by the radiation into 

 the starry spaces aroimd. These spaces are very cold ; and the earth 

 is losing continually a little of its warmth. It is growing colder in 

 its whole mass — slowly indeed, so slowly that the effect has hardly 

 been felt by any change at the surface during all the reach of history, 

 but siu'ely, regularly, and continually ; and this has been the case 

 during all prehistoric periods, while our solar system has been guided 

 along its cold ethereal path. The farther back we go in this con- 

 templation the warmer grows the surface, the greater the flow of 

 heat outwards ; the nearer to the surface any given isothermal line, 

 the smaller the depth at which we should reach the heat of boiling 

 water, of sublimated gases, of fused rocks and metals. As the in- 

 ternal heat certainly, if slightly, now influences and exalts the tem- 

 perature of the surface, it must formerly have influenced and exalted 

 it more. 



But how much more? Can we ascribe to this cause the once 

 elevated temperature of the north temperate and even circumpolar 

 zones of the earth, which seems to be indicated by the cycadaceous 

 plants, the palms, and the tree-ferns, no less than by the coral-reefs 

 and the crocodilian, enaliosaurian, and deinosaurian reptiles of those 

 latitudes in all but the most recent geological periods ? Let us sup- 

 pose that for these effects a general augmentation of 10° to the tem- 

 perature in. the northern regions might have sufiiced in the older 

 periods, the present augmentation of temperature by flow of heat 

 from the interior being -^° ; if the flow of heat depended only on 

 conduction from particle to particle, and bed to bed, it must have 

 been 200 times greater, in a given time, in the early period than at 

 present, and the augmentation of temperature in descending must 

 have been 200 times greater in a given vertical space. Therefore 

 the temperature of boiling water, now perhaps attainable at about 

 10,000 feet, would, under this limitation, have been found at ^-g^^-^ 

 = 50 feet, and all but surface-springs would have been springs of 

 boiling water*. 



* If / denote the excess of the present surface-temperature above the final hmit 

 to which the temperature would descend in an indefinite period of time, and ff 



the rate of increase of temperature, we have - = b, where b is nearly equal to 



unity. — Hopkins, Address to the Geol. Sac. 1852. 



