Springs and Artijicial Foimtains. 271 



area, now by successive accumulations, tHis sand bank forms a hill 

 more than thirty metres in height, where the inhabitants of Alvarado 

 and the crews of the vessels, which frequent this port, daily go to 

 procure water, froni the spring, flowing at its summit, which is fresh 

 dnd'of a good' quality; finally, such is the spring of Lairet, at the 

 chateau' of the Source- J\f or ogues, near Orleans, w^iich rises from a 

 very deep pit, formed of sand on its borders, and of i-ock at the bot- 

 tom, dnd which yields a volume of water of more than tliirty cubic 

 metres. 



33. Volcanic earths and those of ti^achyte^ which are now gener- 

 ally considered as having been thrown out from below the granite, by 

 the action of subterranean fires, afford springs of fresh water, which 

 proceed from infiltrations; their superior parts often present lakes 

 and other large collections of water. Among the numerous exam- 

 ples which we are able to cite, there are none perhaps, more remark- 

 able, than the beautiful springs in the grotto of Royat, which supply ' 

 the fountains of Clermont. Few countries afford so many springs, 

 cts the volcanic mountains of Puy de Dome and of Cantal. 



34. The terrains de trachyte and volcanic ejections contain many 

 mineral and thermal springs, which present, in their temperature and 

 composition^ the same characteristics as those of the primitive earths : 

 thus these waters are more or less charged with sulphuretted hydro- 

 gen, carbonic acid, carbonate of soda, and lime, of silex, &c.; such 

 are those of Mont d'Or, Saint AUyre, Viele-Comte, Chatel-Guyon, 

 near Riom, Chap des Beaufort, and Chalusset, fee &z:c.; the two 

 last are remaikable for the quantity of carbonic acid gas, which is 

 disengaged from tlie earth, from which they issue. As to those of 

 Deux-Landes, which issue from trap rocks, covered by compact cal- 

 careous formations, they present this peculiarity, that at a tempera- 

 ture of 60^, they are almost pure, and contain but a very small quan- 

 tity of magnesia and sulphate of soda. 



35. According to some natural philosophers, the theor}^ of tlie 

 waters rising above the surface of the earth, through perforations 

 made by boring with an auger, has sometimes been considered as 

 analogous to that of jets d'eau, and at others, to that of the syphon. 

 The shaft made by boring, they say, being only the second branch 

 of a great syphon, whose first branch is the subterranean spring, which 

 flowing between the impermeable strata, tliese confined waters pro- 

 ceed from a more elevated region, than that in which tlie boring has 

 been excavated. (Plates L and IL) 



