44 Dr. Mac CuUoch on the Origin of Rocks, Sfc. 



This is one of the unfortunate results that sometimes follows from 

 attempting to prove too much ; from overstraining an argument, 

 so as to give advantages to the adversary, who, in finding a weak 

 point, imagines that one blow will slay his enemy. It is not very 

 good philosophy to disregard an obvious cause for the purpose of 

 adopting a possible one ; and it is a subject for regret, that those 

 to whom geology is indebted for many rational views have too 

 often exposed themselves to this censure. 



But, in admitting that the great mass of secondary strata have 

 been consolidated by a watery agent, it must be remembered that 

 there is a wide difference between the consolidation and the pre- 

 cipitation of the same substances frDm water. If every one of 

 these rocks did not give the most unquestionable proofs of its 

 having originated, either in the ruins of more ancient rocks, or in 

 the spoils of animals, it would be a sufficient argument against 

 precipitation from a watery solution, that it involves every species 

 of chemical and mechanical impossibility that can be included in 

 a proposition so simple. It is unnecessary at present to detain 

 the reader a moment longer on an hypothesis that would create 

 and destroy oceans at its pleasure, yet find them ineffectual. 



No notice has yet been taken of the power of mere pressure, 

 either in actually consolidating rocks, or in assisting their con- 

 solidation. Yet it is an agent not to be overlooked ; and when 

 we consider the enormous weight to which the strata must have 

 been subjected, it is very easy to conceive that its power cannot 

 always have been inefficient. The occasional compression and 

 fracture of imbedded shells, proves that it has sometimes acted; 

 and if even the most delicate of these bodies are generally pre- 

 served, it only proves that they were well supported by the sur- 

 rounding materials, not that they have not been subjected to 

 great pressure. In our own experiments, with forces far inferior, 

 clay can be compressed into a substance as hard as shale ; and 

 there are many of the schists not so hard as the heterogeneous 

 mixture that is forced into a rocket, although composed of mate- 

 rials from which such an effect could scarcely be anticipated. s 

 [This Paper will be concluded in our next Number.] ^ 



