*f - 



160 SANDSTONE PETRIFACTIONS. 



sible by the naked eye, should at once make its way 

 into the interior of the wood, and there take up its 

 residence, accompanied or followed by other pieces of 

 the same kind. No expansion of the vegetable pore 

 that we can conceive, would be adequate to allow 

 this. And, therefore, if the petrifaction of the wood 

 takes place by means of the gradual accumulation 

 and cementation of particles of sand already form- 

 ed ; or, in other words, small pieces of quartz al- 

 ready formed, we must suppose the process to go on 

 in some such manner as the following. The wood 

 dissolves in the surrounding medium, whatever that 

 medium may be ; and there can be no doubt, that 

 the outer parts of it, as being most exposed to the 

 action of the medium, will dissolve first. The par- 

 ticles of sand then take the places of the particles 

 of the wood, and are deposited exactly in the same 

 situation. Moreover, we must suppose, that they 

 are at the same time fixed together by the cement, 

 be this what it will, clay, or marl, or other quartz ; 

 for, if that were not the case, how could the places 

 of the sandy particles be so exactly preserved ? But 

 if they are cemented together as soon as they are 

 deposited, a close coating of sandstone will thus be 

 formed all around the tree ; and how shall the inte- 

 rior of it afterwards be petrified ? The particles of 

 sand can no longer reach it. They cannot make 

 their way through the sandstone already formed. 

 And though we might thus, in some sort, see how 

 a thin coating of sandstone might be deposited 



