CALCAREOUS SPRINGS. 
181 
Sir Humphrey Davy thus describes the proper- 
ties of a small lake in the Campagna between Rome 
and Tivoli : " I 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 
800 of Fahrenheit, and the , quantity of carbonic acid 
that it contains, render it pecuharly fitted to afford 
nourishment to vegetable life. The banks of trav- 
ertin are everywhere covered with reeds, lichen, 
confervas, 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 zoophy tic 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. 
Q 
