FLINT- SINTER OF THE GEYSERS. 00 



owe to pakgonite, — a rock very abundant in this 

 island, but occurring only in a few other places, 

 being a somewhat soluble compound of silica with 

 alumina and alkali. This dissolved silica is the 

 source of the white flint-sinter, which, being 

 deposited by the water about the spring's 

 mouth, gradually raises the ground all round it, 

 hardening it even where it had been formerly 

 a swamp; and so quickly does it spread in some 

 places, that plants still green are found embedded 

 in the flinty mass. Bunsen remarked that by 

 cooling the water no trace of silica was separated 

 from it. Only by evaporating it in a dish some 

 of it was obtained as a fine crust, and that only 

 about the moistened edge of the vessel, where the 

 liquid that had covered it had entirely evaporated, 

 and the liquid itself did not become clouded 

 with the hydrate of silica, till it was very con- 

 siderably concentrated by evaporation. To this be- 

 haviour of the water, Bunsen in part attributes the 

 great variety in the appearance of the hot springs of 

 Iceland. Conceive, says he, a simple petrifying 

 spring which pours out the water from its basin 

 over a smooth, sloping surface of ground; it is 

 clear that the reservoir itself, in which the 

 ever replenished water offers but a very small 

 surface for evaporation, must remain free from 

 siliceous deposits, while its rim, which is just 

 above the level of the water, and over winch the 



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