DR T. THOMSON'S Analysis of some Minerals. 447 



Or, if we consider the sesquichloride as replacing a certain por- 

 tion of sesquisiiicate of iron, then the constituents will be, 



3 atoms sesquisiiicate of iron, 



1 atom sesquisiiicate of manganese. 



11. Sp. Nontronite. Discovered at Nontron, in the Depart- 

 ment of Dordogne, France, and described and analyzed by BER- 

 T-HEIR * Its constituents are, 



7 atoms terpersilicate of iron, 



2 atoms bisilicate of alumina, 

 1 atom silicate of magnesia. 



It might be considered as a compound of two distinct mi- 

 nerals. 



The first composed of 



1 atom terpersilicate of iron. 

 1 atom silicate of magnesia. 



The second of 



3 atoms terpersilscate of iron. 

 1 atom bisilicate of alumina. 



One integrant particle of the first of these, combined with 

 two integrant particles of the second, would Constitute nontro- 

 nite. On this view of its constitution, nontronite might be re- 

 presented by the following formula : 



1 (/S 3 + MS) + 2 (3/S 3 + A / S*) 



* Ann. de Chim. et de Phys. xxxvi. 



