332 Dr Brewster's Description of Levijnc, 



those, whose care in constructing treatises on mineralogy should 

 be to prevent information we are already in possession of, from 

 perishing. Very frequently, indeed, they may be excused for 

 having followed that course, when the description given was 

 so indeterminate, that no remarkable points of difference from 

 other species could be deduced from them, or when no de- 

 scription at all was given. 



Trona has been very much in this situation. I have been 

 indebted to Dr Hope for the specimens which have enabled me 

 to ascertain some of its characters, and so far to supply the 

 defects in the former descriptions, that it may in future be 

 considered as a particular mineral species. The difference 

 between the common carbonate of soda (the hemi-prismatic 

 natron-salt of the method of Mohs) and the Trona of Fezzan, 

 had already been pointed out by Klaproth ; but it seems that 

 even the chemical mineralogists have not paid that degree of 

 attention to his correct determination which it deserves, be- 

 cause there was yet wanting the exact statement of those 

 characters, which it possesses in its natural state, and upon 

 which alone the determination of the species can be founded. 



Art. XXIX. — Description of Levy ne, a Neio Mineral Spe- 

 cies. By David Brewster, LL. D. F. R. S. Lond. and 

 Sec. R. S. Edinburgh. 



1 he mineral of which I propose to give a brief description, 

 was kindly transmitted to me for examination about a year 

 ago, by Mr Heuland. In the memorandum which accom- 

 panied it, Mr Heuland stated that he suspected it to be new, 

 and upon examining its optical properties, and comparing it 

 with those minerals with which it seemed to be most closely 

 allied, I had no doubt that it constituted a new and interest- 

 ing species. 



This mineral occurs in the cavities of an amygdaloidal rock, 

 from Dalsnypen, in Faroe, and sometimes accompanies the 

 Chabasie and Analcime, but particularly a new variety of the 

 Heulandite. 



