230 HOT SPRINGS. 



solution, by the agency of intense heat. Few 

 geologists are aware how large a proportion of the 

 calcareous, magnesian, and silicious rocks distri- 

 buted over our planet, have been deposited from 

 hot springs. Mr. Lyell has shewn, that various 

 parts of Italy and Sicily are covered over by 

 strata of limestone thus formed, several hundred 

 feet deep in many places. 



It is impossible to have enlarged views of 

 chemical science, if we confine our observations 

 to the petty operations of an artificial laboratory. 

 Those who do so might conclude, that silex is 

 insoluble, or nearly so, in water. But those 

 who look to the great laboratory of subterranean 

 chemical action, where the heat is far more in- 

 tense than man can produce, will find that silex 

 is there dissolved as copiously as sugar in boil- 

 ing water ; and that it is deposited in vast quan- 

 tities by hot springs, such as the geysers of Ice- 

 land, the valle das furnas of St. Michael, and 

 innumerable others that issue from volcanic 

 regions, forming opal, chalcedony, and various 

 silicious gems. 



The flinty deposits found in the chalk beds 

 of Europe, have doubtless been derived from 

 submarine hot springs. Many of the marine fos- 

 sils found in the chalk, are composed of silica, 

 a fact which cannot be otherwise accounted for.* 



* It is related by Mr. Barrow, in his Visit to Iceland in 1834, 

 that the streams which proceed from the geysers of Iceland, de- 

 posit a white silicious rock, of a close compact texture, resemb- 



