158 ANALYSIS OF L1THOMA11G1J FROM MAXTON. 



Hcucc the formula representing its composition is, 



2 Al. S* + Aq; 



The formula for those specimens hitherto examined being 



Al. S* + 2 Aq. 



Berthier has included a mineral possessing the same composition under 

 Halloysite, and another under Kaolin, as exhibited in the following table : 



Halloysitc, Fahlun. Kaolin, Normandy. 



Silica, . 46.8 50. 



Alumina, 26.7 28. 



Peroxide of Iron, 5. 5.5 



Magnesia, 0.4 .7 



Lime, . 3. 5.5 



Potash, . 2.2 



Water, 13.5 9.5 



95.4 101.4 



Berthier considers these two specimens as affording instances of fel- 

 spar 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 countenance 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. 



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

 kindness of the Rev. 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, yielding to the finger ; contains greenish streaks and an- 

 swers to the description of Lithomarge or rock-marrow, spec. grav. 2.457. 

 With carbonate of soda, fuses before the blowpipe in the outer-flame in- 

 to 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 



Silica, 



Alumina, 



Potash, 



Lime, 



Magnesia, 



Water, 



100.000 



Its composition is therefore 



Silica, 19 Atoms. Lime, 0.5 atoms. 



Alumina, 7.5 Magnesia, 0.5 



Potash, 1.0 Water, 4.0 



The formula to represent its composition will be 



8J Al. S 2 -f K S 2 -r 4 Aq. 



Under this mineral we may, perhaps, include Berliner's Kaolins from 

 St Tropez and Mende. 



