158 ANALYSIS OF LITHOMAEGE FROM MAXTON. 



Hence tlie formula representing its composition is, 



2 Al. S2 + Aq ; 



the formula for those specimens hitherto examined being 



Al. S2 + 2 Aq. 



Berthier has included a mineral possessing the same composition 

 under Halloysite, and another under Kaolin, as exhibited in the 

 following table : 



Halloysite, Fahlun. Kaolin, Normandy. 



Berthier considers these two specimens as affording instances of 

 felspar in different states of decomposition ; and although he adduces 

 no circumstances which tend to confirm his supposition, yet it is possible 

 his conjecture may be correct. I could observe no fact, however, 

 which could give coimtenance to the idea, that Tuesite, or Fuller's 

 earth, was in any way connected with felspar in masses. 



Analysis of Lithomarge from Maxton. By Robert D. Thomson, M.D. 



Foe this specimen, as well as for the preceding, I am indebted to the 

 kindness of the Eev. John Thomson of Maxton. It occurs in veins in 

 the old red sandstone near the school. It is a soft yellowish substance. 

 It is smooth, jdelding to the finger ; contains greenish streaks and 

 answers to the description of Lithomarge or rock-marrow, spec. grav. 

 2.457. "With carbonate of soda, fuses before the blowpii^e in the outer- 

 flame into an opaque brown bead, becoming colourless on cooling. 

 Does not fuse with borax. With biphosphate of soda, fuses in the 

 outer flame into a transparent colourless bead. Its constituents by my 

 analysis are 



Its composition is therefore 



Silica 

 Alnmina, 

 Potash, 

 The formula to represent its composition will be 



8^ Al. S2 + K S3 4 Aq. 

 Under this mineral we may, perhaps, include Berthier's Kaolins 

 from St Tropez and Mende. 



