THEORY of the EARTH. 257 



be perceived in the polifhed furface of the (lone, by means of 

 the reflection of light. 



THERE is a certain direction in which, viewing the ftone, 

 when the light falls with a proper obliquity, we fee a luminous 

 reflection from the internal parts of the ftone. This arifes 

 from the reflecting furfaces of the fparry ftructure or minute 

 cracks, all turned in one direction, confequently, giving that lu- 

 minous appearance only in one point of view. 



Now, all the parts of the ftone in which the figured quartz 

 is directed in the fame manner, or regularly placed in relation 

 to each other, prefent that fhining appearance to the eye at one 

 time, or in the fame point of direction. But there are parts of 

 the mafs, which, though immediately contiguous and properly 

 continuous, have a different difpofition of the figured quartz ; 

 and thefe two diftinguifhed mafles, in the fame furface of the 

 polifhed ftone, give to the eye their fhining appearance in very 

 different directions. Fig. 3. fhows two of thofe figured and 

 fhining mafles, in the fame plane or polifhed furface. 



IT muft be evident, that, as the cryftallization of the fparry 

 ftructure is the figuring caufe of the quartz bodies, there muft 

 be obferved a certain correfpondency between thofe two things, 

 the alinement (if 1 may be allowed the expreflion) of the quartz, 

 and the fhining of the fparry ground. It muft alfo appear, 

 that, at the time of congelation of the fluid fpar, thofe two 

 contiguous portions had been differently difpofed in the cryftal- 

 lization of their fubftance. This is an obfervation which I have 

 had frequent opportunities of making, with refpect to mafles 

 of calcareous fpar. 



UPON the whole, therefore, whether we fhall confider granite 

 as a ftratum or as an irregular mafs, whether as a collection of 

 feveral materials, or as the feparation of fubftances which had 

 been mixed, there is fufBcient evidence of this body having been 

 confolidated by means of fufion, and in no other manner. 



K k WE 



