128 MR HAIDINGER on the Natural-Historical 



take for granted as a genuine transition, whatever appears to be 

 so to the unassisted senses, or, indeed, what is considered as such 

 in many mineralogical works. A real transition should not be 

 considered to take place, till the differences in each of the single 

 characters, taken separately, have been collected into as many 

 continuous series * ; and before this has been accurately effected, 

 it will in every respect be found more useful for natural history, 

 to consider as particular, although doubtful, species, such varieties 

 as are but imperfectly known, than to unite them with other 

 species, respecting which our information is more complete : for 

 the uncertain existence of a particular species, will always be 

 more apt to induce naturalists to examine more closely the varie- 

 ty in question, than the admitted or supposed want of distinct- 

 ness of some varieties of another species, which has already been 

 correctly described. 



Although HAUY may have traced the connexion between his 

 Diallage verte and some greenish-grey, and blackish varieties, yet 

 a similar passage is entirely wanting among these, and the two 

 subdivisions of his Diallage metallo'ide, the natural-historical spe- 

 cies of diatomous and hemiprismatic Schiller-spar. In the first of 

 these, the Diatomous Schiller-spar, the regular forms are as yet 

 unknown ; but, besides the difference in the hardness of that sub- 

 stance and Green Diallage, it is impossible to join into one 

 continuous series the degrees of their specific gravity. As to the 

 second, or Hemiprismatic Schiller-spar, that identity in the se- 

 ries of crystallisation, which is requisite to establish a transition, 

 is entirely wanting, at least in so far as we are yet acquainted 

 with the forms which it presents. 



The first naturalist who considered Smaragdite as a spe- 

 cies of its own, was the elder SAUSSURE, by whom it was first ac- 

 curately described, and provided with the above-mentioned 



* MoHs 1 Grund-Riss der Mineralogie, Th. i. F. 408. 



