AND ANALOGIES, OF ROCKS. 203 



consequent production of siliceous tufas and stalac- 

 tites. To convert this property to the present pur- 

 pose, it is not requisite that the solution be very ex- 

 tensive, or very rapid. If we conceive this agent 

 operating for a long series of years in a mass of loose 

 sand or of clay, it is not difficult to see that the final 

 result must be, in the first instance, the formation of 

 a sandstone, and, in the other, probably, that of a 

 schist. That this is the fact in nature, is almost de- 

 monstrable from the frequent partial occurrence of 

 sandstones in beds of loose sand, and from the mixed 

 chemical and mechanical texture of almost all the 

 solid sandstones in nature. This effect, it is true, 

 has been attributed by certain philosophers to the 

 action of heat. But to adduce as an agent, that 

 which cannot be shown capable of producing a given 

 effect, while we are in possession of one that has the 

 desired power, is to abandon sound reasoning for the 

 sake of maintaining a species of fictitious analogy, 

 which, after all, is not necessary for the support of 

 that theory by which it was so anxiously defended. 



Thus there have been demonstrated two distinct 

 sets of causes for the formation of rocks; the first 

 chiefly applicable to the unstratified substances, and 

 the last to the formation or consolidation of strata. 



It has been objected to the possibility of aqueous 

 consolidation, by those who have laboured much 

 more to dictate a system of geology than to deduce 

 one, that a liquid solvent could not exclude itself 

 from the pores of the rock after depositing the conso- 

 lidating matter; that it should therefore remain 

 within the stone, or else leave the body pervious to 

 water ; " neither of which is" said to be " the fact." 

 On the contrary, both of these are facts. That which 

 was asserted not to exist, by those who did not know 



