326 



/ 



mits the power in heat, of promoting the solution ; yet he remarks, 

 that experience has shown, that an actual solution of silex in sim- 

 ple water takes place, not only in springs, the natural temperature 

 of which is much inferior to the ebullient heat of those in Iceland, 

 but also in several other mineral waters : and even that some com- 

 mon sweet-water springs contain dissolved silicious earth. 



In corroboration of the opinion, that the induration of various 

 substances may have been derived from the deposition of silicious 

 matter, from its solution in water, I must call your attention to the 

 silicious tufa which is deposited by the Icelandic hot-springs ; in 

 the same manner as the calcareous tufa is deposited by mineral 

 springs impregnated with lime, as in those of Matlock. A bason 

 of 60 feet in diameter, the outer border of which is 9 feet above 

 the opening of the pipe, as well as the pipe itself, which is 19 feet 

 in diameter, and which, from its depth being unknown, is consi- 

 dered by the Icelanders as the gate of hell, are entirely formed by 

 deposition from the boiling water of the Geyser, which is sometimes 

 thrown out, from this enormous opening, to above the height of 100 

 feet. This tufa having been analysed by Mr. Klaproth, was found 

 to consist of. 



Gr. 



Silex 98 



Alumine 1.50 



Oxide of iron . . .50 



100* 



M. Gensanne relates, that in the mines of Cramaillot, in Tranche 

 Gompte, stalactitic concretions of silex form on the vaults of the 

 works, from the transuding water ; and that they are sometimes 

 found on the timbers of the mine +. 



* Analytical Essays, p. 408. 



f Histoire de Languedoc, torn. ii. p, 28. 



