3S8 ON THE PRIMITIVE FORM OF CRYSTALS. 



such as Chromate of Lead, Mesotype, Sulphate of 

 Magnesia, &c. had actually two axes, while Ido- 

 crase and Titanite had only one, T was compelled 

 to suppose that these two last crystals must belong 

 to a different primitive form, though I at the same 

 time remarked, on the strength of the general prin- 

 ciple, " That it was within the limits of pro- 

 bability that all the crystals which I had ranked 

 under the Right Prism might have another Pri- 

 mitive Nucleus. 49 



This opinion ceased to be a conjecture, when 1 

 found that the primitive form of Mesotype and 

 Needlestone was a Right Prism with a Rhombic 

 Base ; and it acquires additional probability when 

 Chromate of Lead was found by M. Soret to have 

 an Oblique Rhomboidal Prism for its fundamental 

 Crystal * 



As all the mineral bodies, therefore, which I had 

 arranged under the Right Prism with a Square 

 Base, have been removed to other primitive forms, 

 the general explanation which I have given in 

 my former paper f , is now without an exception ; 

 and the First Class of Primitive Forms will now 

 include the Right Prism with a Square Base, 

 and will stand thus : 



* This had formerly been the opinion of Bournon ; (see 

 his Catalogue, p. 355.) and Haiiy now considers it as correct. 

 See Annates ties Mines, 1818,, torn. iii. p. 479- 

 t See page 68. 3 



