It appears that there are extensive districts in various parts
of Europe, where, under certain conditions of geological
structure, and at certain levels, artificial fountains will rise
to the surface of strata which throw out no natural springs,[1]
Notices scientifiques par M. Arago. Annuaire, pour l'An. 1835.
Von Bruckmann uber Artesische Brunnen. Heilbronn am Neckar, 1833.
- ↑ The Diagrams in Pl. 69. Figs. 1 and 2. are constructed to illustrate the causes of the rise of water in natural, or artificial springs, within basin shaped strata that are intersected by the sides of Valleys, or traversed by Faults.
Supposing a Basin (Pl. 69 Fig. 1.) composed of permeable strata, E. F. G. alternating with impermeable strata, H. I. K. L. to have the margin of all these strata continuous in all directions at one uniformly horizontal level, A, B, the water which falls in rain upon the extremities of the strata E, F, G, would accumulate within them, and till all their interstices with water up to the line A, B; and if a Pipe were passed down through the upper, into either of the lower strata, at any point within the circumference of this basin, the water would rise within it to the horizontal line A, B, which represents the general level of the margin of the Basin. A disposition so regular never exists in nature, the extremities or outcrops of each stratum are usually at different levels, (Fig. 1. a. c. e. g.) In such cases the line a. b. represents the water level within the stratum G; below this line, water would be permanently present in G; it could never rise above it, being relieved by springs that would overflow at a. The line, c. d. represents the level above which the water could never rise in the stratum F; and the line e, f, represents the highest water level within the stratum E. The discharge of all rain-waters that percolated the strata, E, F, G, thus being effected by overflowing at e. c. a.
If common wells were perforated from the surface, i. k. l. into the strata G. F. E, the water would rise within them only to the horizontal lines a, b, c d, e, f.
The upper porous stratum C, also, would be permanently loaded with water below the horizontal line, g, b, and permanently dry above it.
The theoretical section, Pl. 69. fig. 2. represents a portion of a basin intersected by the fault H, L, filled with matter impermeable to water. Supposing the lower extremities of the inclined and permeable strata N, O, P, Q, R, to be intersected by the fault or dike H, L, the rainwater which enters the uncovered portions of these strata between the impermeable clay beds, A, B, C, D, E, would accumulate in the permeable strata up to the horizontal lines, A A″, B B″, C C", D D″, E E″. If an Artesian well was perforated into each of these strata to A', B', C', D', E', through the clay beds A, B, C, D, E, the water from these beds would rise within a pipe ascending from the perforations to the levels A″, B″, C″, D″, E″.
These theoretical Results can never occur to the extent here represented, in consequence of the intersections of the strata by valleys of Denudation, the irregular interposition of Faults, and the varying conditions of the matter composing Dikes.
If a valley were excavated in the stratum M below A″, the water of this stratum would overflow into the bottom of this valley, and would never rise on the side of the fault so high as the level H.
Wherever the contact of the Dike H, L, with the strata M, N, 0, P, Q, R, that are intersected by it, is imperfect, an issue is formed, through which the water from these inclined strata will be discharged at the surface by a natural Artesian well; hence 9, series of Artesian springs will mark the line of contact of the Dike with the fractured edges of the strata from which the water rises, and the level of the water within these strata will be always approximating to that of the springs at H; but as the permeability of Dikes varies in different parts of their course, their effect in sustaining water within the strata adjacent to them, must be irregular, and the water line within these strata will vary according to circumstances, between the highest possible levels, A, B, C, D, E, and the lowest possible level H.
