152 T. Mellard Reade—The Age of the World. 



Eeasoning from observation, as a geologist is bound to do, the 

 greater probability is that the surface would become crusted over in 

 a way that the lava in a volcano becomes crusted over, and that the 

 surface rock would be of a vesicular character of less specific gravity 

 than the molten matter. Nasmyth's theory of the volcanos of the 

 Moon^ is founded on the supposition that the molten matter expands 

 in cooling, giving examples in support of his idea, such as the fact 

 that a lump of cold cast-iron will float in molten iron. Sir W. 

 Thomson assumes the rock will cool, contract and sink in the molten 

 mass. Which is right ? Nasmyth certainly has had the most 

 practical experience of molten metals ! That a cooling globe solidi- 

 fies from the surface, I think the Moon is a striking proof.^ 



The crust would most probably solidify and break up again and 

 again, and hot materials be injected into, through, and on to the 

 surface. 



A glance at a map of the volcanos of the Moon should satisfy 

 any one on this point, for there are the evidences of almost countless 

 myriads of volcanic rings or craters, covering the whole surface and 

 superimposed or breaking through one another in a most remarkable 

 way. Observation, then, tells us that a crust will most likely form 

 on a globe of molten rock. Now, in the case of the Earth, comes 

 in the question of denudation ; for no sooner is a sufficient crust 

 formed than the aqueous vapours and atmospheric agencies begin to 

 eat it down, and thus we have a composite crust of sedimentary and 

 A'olcanic materials, such as the geologist is acquainted with as exist- 

 ing in Nature. There is also this fact in favour of a retention of 

 heat by the globe, that pumice rock, and any rock of a loose or 

 vesicular nature, possesses small conducting power, — the proportion 

 of absolute resistance to the passage of heat being as 1818 in dry 

 pumice to 87 in rock-salt. 



The laminations and alternations of beds is also, I strongly believe, 

 favourable to the retention of heat,^ so that we see a coating must be 

 gradually formed round our incandescent globe like the felt round a 

 steam boiler. 



This speculation, though interesting, is rather outside of true 

 geological inquiry ; it is beginning at the wrong end. No one yet 

 has ever had a glimpse of this primitive globe ; for though we have 

 a knowledge of a thickness of rock estimated at from 14 to 17 

 miles, the base is practically the same as the topmost story of the 

 superstructure. These original crusts have most likely been broken 

 up, melted and destroyed long since, as sediments have been also 

 melted and destroyed. 



Much more may be said on the subject, but I trust enough has 

 been shown to prove that the hypothetical way of treating such 



^ The Moon as a Planet, as a World, and a Satellite, Nasmyth and Carpenter. 



^ Mr. Mallet has controverted Nasmyth's conclusions, Proc. Eoy. Soc. 1874, 

 p. 366. Nevertheless, he admits the fact of certain pieces of cold cast-iron floating 

 upon molten iron. 



3 In my Presidential Address to the Liverpool Geol. Soc. Session 1875-6, "On the 

 Moon and the Earth," it is suggested, p. 89, that " the sediments accumulating on 

 the Earth from age to age must act as a non-conducting envelope." 



