306 Analyses of Books. [Oct. 



be the case when matter is deposited upon an inclined plane. 

 The bed ought to be thickest at the bottom, and thinnest at the 

 summit of the inclined plane on which it is deposited. This 

 sometimes happens, and indicates obviously the cause from 

 which it results. 



6. The thickness of masses often varies considerably in differ- 

 ent parts of their course. This is well known to be the case 

 with the coal beds. 



7. The term stratification is connected with theory. Many 

 persons think that rocks are not stratified unless they have been 

 deposited from a fluid menstruum. They conceive that the strata 

 are produced by depositions alternately suspended and renewed. 

 But our author considers it as certain that this is not always the 

 case for the following reasons : 



(1.) Parallelism of surface may be produced by other causes, 

 as in basalt, tabular flint, &c. 



(2.) The recurrence of parallel planes depends upon the 

 substances deposited. Granite, porphyry, trap, salt, chalk, are 

 always in thick masses ; argillite in flakes ; sandstone and oolite 

 in beds. 



(3.) The larger divisions of rocks are frequently not parallel 

 to the laminae of which these rocks are composed. 



(4. V Way-boards depend upon the nature of the rock : stony 

 beds have them ; while sand-clays, loams, &c. are destitute of them. 



(5.) At the junction of two kinds of rock, as greywacke slate 

 and limestone, we find that each is impregnated with the sub- 

 stance of the other. 



(6.) The contemporaneous veins of one stratum sometimes 

 extend themselves into the adjoining stratum. 



(7.) Decomposition or torrefaction often expose to view stra- 

 tification which was before latent. 



(8.) Depositions which go on uninterruptedly in our laborato- 

 ries frequently arrange themselves in distinct layers. 



These reasons in order to produce conviction would require to 

 be much more developed than the author has thought requisite. 

 Indeed I must acknowledge that I do not perceive the force of 

 some of them, nor the truth of others. I should like to know, 

 for example, what uninterrupted depositions in chemical labora- 

 tories take place in distinct layers. I am not aware of any 

 example of this in crystallizations. Mechanical deposits doubt- 

 less arrange themselves in layers when they differ considerably 

 in their specific gravities ; but such depositions are not entitled 

 to the name of chemical. They are entirely owing to the action 

 of gravity, and accordingly follow the order of their specific 

 gravity. Geologists have not attended sufficiently to the differ- 

 ence between crystallization and mechanical deposition. When 

 the Wernerians say that granite is stratified, and at the same 

 time that it was separated from a fluid by crystallization, I am 

 of opinion that they are guilty of a contradiction in terms. 



