\Hot and Thermal Springs, 558 



phates, together with iron and an organic substance, iron-pyrites 

 is very easily formed, and in this manner they may fill up their 

 subterranean channel. This may also happen when two diffe- 

 rent mineral springs meet in one cleft, one of which contains car- 

 bonate of protoxide of iron, and the other a sulphate and an or- 

 ganic substance. And nothing is more common in mineral 

 springs than these substances. In general, many cases may be 

 imagined, in which the confluence of mineral springs composed 

 of different ingredients might occasion such sediments as would 

 by degrees fill up their passage. For example, if springs con- 

 taining earthy salts should meet with others containing alkaline 

 carbonates ; or if waters rich in silica * should meet with organic 

 substances, whether in solution, or in the solid state, by which, 

 as I have shewn, siliceous concretions would be formed. 



In the above mentioned sulphurous springs of the East Pyre- 

 nees, iron-pyrites and earthy carbonates might easily be formed at 

 the expense of their sulphuret of sodium and thair alkaline carbon- 

 ates, by their meeting with other springs containing salts of iron 

 and earths, and thus the channels of these springs becoming gra- 

 dually filled from the bottom, the waters would by degrees be 

 enabled to sink less and less deep into the earth, f 



Lastly, an obstruction in the course of the springs may be oc- 

 casioned partly by chemical and partly by mechanical means. I 

 have pointed out j: several appearances which make it seem very 

 probable, that ferruginous waters act as a cement upon loose 

 stony materials, namely, upon sand, and may thus give rise to 

 the formation of stony concretions. There is no doubt that wa- 

 ters containing much sihca occasion siliceous concretions, such as 

 are found very characteristic in the sandstone belonging to the 

 lignite (braunkohl) formation, and also in other positions. And 

 surely concretions of this kind may also easily be formed in the 



■ In the great Geyser, the deposits of silica have accumulated in a crack to 

 the thickness of 12 feet. 



t Supposing the increase of temperature in plains and in enclosed valleys 

 to amount to 2°^ in 1 15 feet, it is easy to perceive, that if the lower parts of 

 a spring's course he very narrow, and the spring be rich in any substance easy 

 to be precipitated from it, no great length of time will Le required to etfecl 

 a perceptible decrev.e of temperature. 



X Schwegger-Seidcls n. Jahrb. der Chemie & Phys. voL viii. p. 437. 



