T. Mellard Reach— The Age of the World. 153 



problems, however clever, ingenious and interesting, is unreliable. 

 Geology demands that a thing should be tested as you go along ; for 

 so little is really known of the physics of the Earth that we continu- 

 ally find facts in discordance with preconceived notions, though, 

 when once known, it is easy to see that such and such a thing might 

 have been predicted by theory. 



It is proverbially easy to prophesy after a thing has happened, and 

 it is just as easy to see that any proved fact is in accordance with the 

 laws of physics. Nevertheless, the observer is continually discovering 

 new things that no one predicts. If there is any one thing that 

 physicists ought to have predicted, it is that the bottom of the ocean 

 is uniformly occupied by water of a very low temperature. Now I 

 think there are few physicists who would not have supposed that the 

 secular cooling of the Earth would, to some degree, have influenced 

 the bottom water of the ocean that must have travelled thousands of 

 miles in contact with it, yet the Challenge^- temperature soundings 

 prove that it has no appreciable effect.^ 



It is impossible in this space to explain the way the geologist 

 approximates to the immense age of the Earth, and as I have already 

 elsewhere^ attempted the calculation on a geological basis, it is thus 

 less necessary for me to do so now. A calm investigation of all the 

 multitudinous facts which necessarily enter into the problem satisfies 

 me, at all events, that no case has been made out for restricting the 

 age of the Earth below that demanded by Geology, even on the 

 assumption of a globe of molten materials to commence with. 

 According to Sir W. Thomson's expressed opinion, "The general 

 climate cannot be sensibly affected by conducted heat at any time 

 more than 10,000 years after the commencement of superficial 

 solidification." So that as the rate of deposition of sedimentary 

 rocks cannot by this hypothesis have been affected by the interior 

 heat of the Earth, it tends to show it is a reasonable assumption on 

 the part of the geologist that the rate of formation of these rocks, 

 dependent on atmospheric degradation, was in former ages very 

 much what it is at present.^ 



I am also of opinion that the rate of increase of underground 

 temperature has, probably, been for long ages past very much what 

 it is now ; for if I have shown that the interior heat of the Earth is 

 introduced into the crust by intrusion, as well as by conduction, there 

 is even now, according to Sir W. Thomson's showing, a vast reservoir 

 of unexhausted heat ; nor must we forget that the present crust of 

 the Earth is not an originally formed product, but one built upon 



1 Mr. Croll (Climate and Time) attempts to explain why tlie secular cooling of 

 the Earth does not affect the hottom water of the Ocean, but the explanation comes 

 after the knowledge of the fact. 



2 " On Geological Time," Presidential Address, Liverpool Geol. Soc. Session 

 1876-7. 



2 Sir W. Thomson, however, infers, that as the Sim must have been hotter in former 

 ages, the atmospheric agencies were then more potent; but this is all pure hypothesis, 

 no proofs that they were being adduced. Mr. Croll again has his own hj'pothesis on 

 the subject, but the fact is we know absolutely nothing of the Sun's heat, and cannot 

 safely reason on conjectures. 



