CALCAREOUS SPRINGS. 



181 



Sir Humphrey Davy thus describes the proper- 

 ties of a small lake in the Campagna between Rome 

 and Tivoli : " 1 have found by experiment that the 

 most tranquil part of the lake, even after being 

 agitated and exposed to the air, contained in solu- 

 tion more than its own volume of carbonic acid gas, 

 with a very small quantity of sulphuretted hydrogen. 

 Its high temperature, which is pretty constant at 

 80° of Fahrenheit, and the quantity of carbonic acid 

 that it contains, render it peculiarly fitted to afford 

 nourishment to vegetable life. The banks of trav- 

 ertin are everywhere covered with reeds, lichen, 

 confervae, and various kinds of aquatic vegetables ; 

 and at the same time that the process of vegetable 

 life is going on, the crystallizations of the calcare- 

 ous matter, which is everywhere deposited in con- 

 sequence of the escape of carbonic acid, likewise 

 proceed. There is, I believe, no place in the world 

 where there is a more striking example of the op- 

 position or contrast of the laws of animate and in- 

 animate nature, of the forces of inorganic chemical 

 affinity, and those of the powers of life."* 



Mr. Lyell supposes that the zoophytic and shelly 

 limestones, which constitute the coral reefs of the 

 Indian and Pacific Oceans, are supplied with car- 

 bonate of lime and other mineral ingredients from 

 submarine springs, and that their heat, as well as 

 their earthy and gaseous contents, may promote 

 the development of corals, sponges, and testacea, 

 just as vegetation is quickened by similar causes 

 in the lake above described by Sir Humphrey Davy. 

 Sulphate of lime or gypsum is deposited by these 

 springs, which are, however, few in number, which 

 contain sulphuric acid and sulphuretted hydrogen. 

 Marl is a deposite of carbonate of lime from ancient 

 lakes or seas. 



Silicious Springs. — The quantity of other mineral 



* Consolations in Travel, p. 123. 



