UNDERGROUND WATERS AS SOCIAL FACTORS. 613 



farther down, -without apparently having received any new supply. 

 The inexhaustible abundance of this interior sheet also receives here 

 an agricultural application which is, perhaj^s, to the present time, 

 unique. The water which is drawn from it by means of shallow wells 

 cOiWed. fontanelle is, in consequence of its nearly constant temperature, 

 which is higher in winter than that of the ambient air, eminently 

 suitable for irrigation. By forcing it to flow constantly in a thin 

 sheet over the ground, the peasants are able, in a cold country, to cut 

 their grass in January as in the summer-time. There are more than 

 a thousand of these artificial subsoil springs, occupying a zone about 

 two hundred kilometres long, extending from Ticino to Verona. 



All rocks which are penetrable to water by means of fissures are 

 also capable of containing phreatic water. The water in these sheets 

 is not stagnant, but is animated by a slow and continuous motion. 

 Among the facts that prove this we may cite the transportation in 

 the subsoil of impurities like coal-tar, in the same direction, over 

 several hundred metres, in a series of wells, the alignment of which 

 marks the direction of the current. This movement is due to the 

 general incline of the sheet. 



In volcanic masses, the scoriaceous dejections and the lava-flows, 

 with their cavities of various dimensions, offer no less facility for 

 infiltrations. Rain-waters penetrate them and reappear lower down. 

 Among the flows of fifty volcanoes in Auvergne, that which issues 

 from the Puy de Gravenoire, near Clermont, gives rise to three 

 springs: first at Fontanat; then at Royat, where they issue from a 

 cave opened in the scoria surmounted by prismatic lava; and at the 

 lower end of the flow the water is discharged under similar conditions 

 to the advantage of the city of Clermont. In the same way, after 

 having formed at Murois those scoriaceous caves to which George 

 Sand has lent an infernal aspect, the long flow of the Tartaret gives 

 out in its course a series of springs, around which several villages have 

 grouped themselves. Thus fire is found to prepare the way for water 

 by creating subterranean conduits for it. 



The natui'al action of the waters which we have studied in the 

 superficial deposits is indicated with equal clearness at a greater 

 depth, in the midst of the stratified rocks. In these last, in fact, 

 certain beds, very penetrable to water, alternate with others which 

 arrest its passage. Whether the beds be horizontal or inclined, the 

 relief of the soil is frequently so gashed that the impermeable support 

 of the filtering and water-bearing stratum crops out and determines a 

 flow by virtue of hydrostatic laws. These natural reservoirs thus pro- 

 duce springs which are permanent, provided successive rains furnish 

 a sufiicient supply of water, while they also sometimes simply give 

 place to irregular oozings. These effusions occur not on the continents 

 only, but also in sea-basins. 



The sedimentary rocks, in their great thickness, inclose a succes- 



