178 



CALCAREOUS SPRINGS. 



with strata filled with cold water, they would give 

 rise to thermal springs of every degree of tempera- 

 ture. 



Calcareous Springs.— 'OviX chief object in noticing 

 springs in this place is to point out how they are 

 agents in the formation of rocks : and we first call 

 the attention of the reader to those charged with 

 lime or calcareous matter, as the phenomena con- 

 nected with them are of high interest in geology. 

 It is a fact generally known, that water has the 

 property of dissolving the calcareous rocks over 

 which it flows. Springs that contain carbonic acid 

 in solution are capable of dissolving a much larger 

 quantity of calcareous matter than rain water; and, 

 owing to the dissipation of the acid in the atmo- 

 sphere, such springs throw down large quantities 

 of lime, in the form of a loose and porous rock, call- 

 ed tufa, or in a more compact form, called travertin* 

 Such springs are more commonly found in lime- 

 stone districts, though not confined to them ; for in 

 Clermont, near Central France, one of these springs 

 issues from a volcanic rock resting on granite, which 

 has formed, by its deposites, a mound of white con- 

 cretionary limestone 240 feet in length, 16 feet high, 

 and 12 wide. 



Among the Apennine hills in Italy, and espe- 

 cially in Tuscany, so much calcareous matter has 

 been deposited by the innumerable springs scatter- 

 ed over the country, that the whole ground is cov- 

 ered with limestone, and sounds hollow beneath 

 the foot. In other places in the same country, Mr. 

 Lyell states that he saw compact rocks formed in 

 this manner, descending the slanting sides of hills 

 much in the manner of lava currents, except that 

 they were of a white colour, and terminate abrupt- 

 ly when they reach the course of a river. 



* This stone was called by the ancients lapis Tiburtinus, being 

 formed in great quantity by the river Anio, at Tibur, near Rome. 

 Travertin is an abbreviation from Transtiburtinns. 



