0;z a new Variety cfEpldote. ' ^« 



This form, which has not yet been defcribed amone the 

 known varieties ot the cpidote, refults: 



ill, From a decFemciit by one row on the edges G of the 

 prilm (Ijg-. 3.) correlpondingto the acute angles" of the bafe. 



2d, From a mixt decrement on the left, by four rows in 

 breadth and three in height, on the other edges H. . 



3d, From a decremcm by three rows to the left on the 

 fame edges. This is that which conftitutes the new variety. 



The' pi'ecc'ding laws do not mark entirely the planes M 

 and T. 



4th, In the laft place, from a decrement by one row on 

 the acute angles E of the rhombus of the bafe. The latter 

 reaching its limits, makes the face P difappear entirely. 



It follows from this ftruclure that the charaAeriliic fio-n 



of the,:"c)r.yftal will be G M % H T E; and the form pro- 



r M t X -r .. ■ ■ ' 



duccd behig a prifm often planes and diedr-al fum,mit5i'{fig.4.), 

 we may thence deduce the denomination of qtiadfidccinial, 

 which will exprefs the four faces of the fummits and the tcA 

 of" the prifm. 



Calculation has given for-tfie inrlinatton ofthc'fVce x pro- 

 duced on the adjacent plane M 63° 23', and oii the declin- 

 ing plane T 131° ^J'^, refults which are agreeable to thofe 

 obtained by geometry. 



Independently of the form already defcribed there have 

 been obferved alio feconc'ary crylials prefcntina; at their fur- 

 face parallel ftriae. This, no doubt, is. that^dcfcribcd by 

 SauHure in the following words : Jlrlts, as if in the form af 

 hajiions. In a word, we may mention as pfeu^omorphic the 

 forms of emarginated garnet, to which this cpidole of Dif- 

 fentis has been alfociaied; for fomctimos it covers it entirelv 

 by being moulded over it, and fontetimes it is completely 

 covered by it in fuch a manner, that one qf tjie two fub- 

 ftanccn cannot be fcen but by liie frafture of the other. 



The obfervation of tliis new vaiiety proves that the detcr- 

 miaaiion of mineral iubftances merely by their exterior cha- 

 rartcrs is exceedingly defcftive ; for the latter b-v. \\s faces is 

 very diftinft from the fpecies to which it belntvrs, but tho 

 geonn-irlc characters aflign to it in the meihoJic.il fyftcm iu 

 real place. 



We (liall remark alfo that the cpidote is a fubf^ancc the 

 varieties of which dilfer from each other actordiug to the 

 countries where they have been found : to becoiivitwcd of 

 this, nothing will be nccelfary but to con)pare that of Dau- 

 pbiny with t?iat of Arcndul and that of Ditlcniis. Their 



ulpeCl 



