38 On the Chemical Composition iifHarmotome. 



Wernekinck. But when we substitute bar)'ta for lime and pot- 

 ash, the formula will not exactly apply to any of the analyses 

 of barytic harmotome with which I am acquainted, although 

 it does not deviate very much from some of them. We can- 

 not, however, I think, draw any argument against the appli- 

 cation of the doctrine of replacement to these two varieties, from 

 this want of perfect conformity ; because the different analyses of 

 barytic harmotome, scarcely vary more from the formula than they 

 do from one another, and we might as well argue that the different 

 specimens of barytic harmotome which were the subjects of 

 these analyses, were not the same mineral, as deny the occurrence 

 of replacement between the two varieties, on the mere ground 

 of this disconformity. On the other hand, the almost perfect 

 identity between the forms of the two varieties, the approxima- 

 tion between their atomic constitution on substituting one set of 

 oxides for another, and the occurrence of small quantities of 

 potash and hme in the barytic harmotome of Strontian, and of a 

 little baryta in the lime and potash harmotome of Annarode *, 

 appear all to render it extremely probable that the two will ul- 

 timately be found to admit of the application of the principles 

 of isomorphism, or at least of piesiomorphism. We may hope 

 that future and more extended analyses will yet establish the 

 perfect conformity of the constitution of barytic harmotome with 

 that of the other variety, on making the requisite substitution. 

 If this shall be the case, we can hardly doubt that the mineral, 

 which has been in this country called Phillipsite, ought also to 

 be considered as a lime harmotome. The general form of its 

 crystals, as described by Mr Levi f , is the same as that of ba- 

 rytic harmotome ; and the measurements of its angles do not 

 present greater discrepancies than between the carbonates of 

 lime, iron, manganese, and magnesia, substances which, if the 

 doctrine of replacement has any foundation at all, must be view- 

 ed as composed of plesiomorphous bodies. Neither would it 

 seem that the variations of its cleavage can present any serious 

 obstacle ; for cleavage appears chiefly of importance as being in-^ 

 dicative of crystalline form ; and as long as the cleavage of two 



• See "Wemekinck's analysis, afterwards given, 

 f Aiuials of Philosophy, November 1825. 



