136 On the Law of Syinmeiry^ 



and where the presence of a foreign body cannot be detected, 

 nuclei of a pecuhar character may often be discovered, which, 

 by all the phenomena they present, we should infer to be centres 

 of emanation from which the crystalline arrangement was gra- 

 dually diffusing itself over the whole formation, so as, in the 

 course of time, to assimilate what is now a mechanical deposit 

 to the more ancient strata. If it be said by any one, that, in 

 order to such a process as the change of mechanical into crystal- 

 line strata, heat is necessary, I will not deny it : but is there not 

 heat enough in every stratum, as it exists at present, to effect 

 this transition, if time enough be supplied ? 



In water, then, and in the solid strata, we see that there ei- 

 ther is already a crystalline or symmetrical arrangement among 

 the constituent particles, or a determination towards such a state. 

 But, in order to learn the law more minutely by which the ag- 

 gregation of the particles of bodies is regulated, we must de- 

 scend from generals to particulars, and enter somewhat more 

 into the details of crystallography. Now, in the case of water, 

 it has been already said, that, where there are fewest obstruc- 

 tions to the action of the individualizing power, the symmetry 

 which results is the most perfect. The same truth, also, is so 

 universally displayed in the processes of the laboratory during 

 artificial crystallizations, that I presume it need not be dwelt 

 upon. But let us see what evidence the mineral kingdom sup- 

 plies of it. 



Now, in the case of imbedded crystals^ we cannot but regard 

 the individual as more perfect, than in the case of imphinted 

 ones, and, consequently, the individualizing power as having 

 taken effect more fully. Are imbedded crystals, then, more 

 symmetrical than implanted ones.'^ The fact is so certain, that 

 the question seems needless. But this is not all. It is a very 

 important fact, for the illustration of our subject, that the actual 

 form of a crystal, vieived as complete^ is almost invariably more 

 symmetrical than the primary or cleavage form. But, in order 

 to illustrate this position^ which may not be so readily assented 

 to, it is necessary, in the first place, to inquire as to what form 

 is entitled to be regarded as the most symmetrical. 



To answer this inquiry, however, it is only necessary to con- 

 sider, that our idea of symmetry is merely similarity of relation- 



