classificatio:n^ m lithology. — general conclusions. 53 



Sectiox IX. — General Conclusions in Bcffard to Systems of Lithological 



Classification. 



The general results and bearing of the preceding can be briefly summa- 

 rized as follows : — 



As is claimed for the organic world, so there is for the inorganic universe 

 a universal law of evolution or development expressed by the phrases : 

 degradation and dissipation of energ//, the passage of the imstaJ)le toivards the more 

 stable condition, — a law under Avhich the universe has moved forward or 

 " run down " from the beginning, and under which its course will continue 

 uniformly to the end. 



True and natural classification and work ought to give expression to that 

 law and conform to it, and the classification and arrangement herein fol- 

 lowed is an effort towards that end. In accordance with this, petrography 

 seems to demand a former liquid globe and one whose interior portions are 

 either now liquid, or in such a condition that they can readily become so. 

 If the so-called physical and mathematical demonstrations of the earth's 

 solidity be examined, it will be found that they have been based on certain 

 hypothetical globes, of a constitution unlike that of the earth, and therefore 

 not applicable to it, but to the hypothetical globes only. On examining 

 the claim that the materials of which the earth's interior is supposed to be 

 composed would tend to solidify under pressure, because they contract in 

 passing from the liquid to the solid state, it is found that the best and more 

 recent observations which compare the relation of the solid and liquid form 

 — both taken at a temperature near the melting point — either prove or 

 render it probable that iron and the various rock materials which are 

 believed to compose the /«/"r«-sedimentary portion of the earth expand on 

 passing from the liquid to the solid. Hence, according to Thomson's law, 

 pressure would tend to render the earth's interior liquid instead of solid. 



The alleged sinking of the earth's crust to the earth's centre could not, 

 according to the above, take place ; since the solid would be lighter than the 

 liquid portion in contact with it. But if the crust were heavier it could not 

 sink far, unless the earth was of homogeneous material ; but since we know 

 it to be heterogeneous — the materials varying also in specific gravity — 

 the crust on sinking would soon meet with material of higher specific 

 gravity, which would prevent any further subsidence. So, too, the heat 



