ON THE OPTICAL PECULIARITIES OF THAT MINERAL. 335 



selected the materials, measured the spaces they were to occu- 

 py, and, finally, combined them into the finest specimen of na- 

 tural Mosaic. 



Those irregularities of crystallisation which are known by 

 the name of Made or Hemitrope forms, and those compound 

 groups which arise from the mutual penetration of crystals, 

 are merely accidental deviations from particular laws, which go- 

 vern the crystallisations in which they occur. The aberrations 

 themselves testify the predominance of the laws to which they 

 form exceptions, and they are susceptible of explanation by 

 assuming certain polarities in the integrant molecules. The 

 compound structure of the Apophyllite, however, cannot be 

 referred to these capricious formations. It is itself the result 

 of a general law, to which there are no exceptions, and when 

 more deeply studied, and better understood, it must ultimate- 

 ly lead to the introduction of some new principle of organisa- 

 tion, of which crystallographers have at present no concep- 

 tion. 



The difficulty of accounting for the formation of Apophyl- 

 lite, is in no way diminished, by giving the utmost licence to 

 speculation. We cannot even avail ourselves of the extrava- 

 gant supposition of a crystalline embryo, which, like that of 

 animal and vegetable life, gradually expands to maturity. 

 The germ of plants and animals is nourished by a series of or- 

 gans, of which, however recondite be the operation, we yet see 

 the action, and witness the effects ; but, in the architecture of 

 Apophyllite, no subsidiary organs are seen. The crystal ap- 

 pears only in its state of perfection ; and we are left to admire 

 the skill which presided at its formation, and to profit by the 

 instruction which is so impressively conveyed by such myste- 

 rious organisations. 



vol. ix. P. ii. u u DE- 



