some Silicates of Alumina, 



363 



Berthier has included a mineral possessing exactly the 

 same composition, with less water, under halloysite, and 

 another under kaolin, as is exhibited in the following table :* 



95-4 101-4 



Berthier considers these two specimens as affording 

 instances of felspar in different states of decomposition, 

 and, although he states no circumstances which tend to 

 establish his supposition, yet it is possible his conjecture 

 may be correct. I could observe no fact, however, which 

 could give the slightest countenance to the idea, that 

 Tuesite or Fuller's earth, but more especially the former, 

 are in any way connected with felspar. 



3. In the sand-stone, which has been already described, a 

 soft whitish substance occurs. It is smooth, yielding to 

 the finger, containing greenish streaks, and answers to the 

 description of lithomarge or rock marrow. The specific 

 gravity is 2*457. Its constituents are, according to my 

 analysis, 



99-900 



Its composition, including the lime and magnesia with 

 the alumina, is expressed by the formula, 

 8J Al S2 -f K S2 + 4 Aq. 

 Berthier analyzed two Kaolins which approach litho- 



• Traite des Essais, i. 60. 



