Geology and Mineralogy considered with reference to Natural Theology/Chapter 22
CHAPTER XXII.
Adaptations of the Earth to afford supplies of water through the medium of Springs.
As the presence of water is essential both to animal and vegetable existence, the adjustment of the Earth's surface to supply this necessary fluid, in due proportion to the demand, affords one of the many proofs of Design, which arise out of the investigation of its actual condition, and of its relations to the organized beings which are placed upon it.
Nearly three-fourths of the Earth being covered with Sea, whilst the remaining dry land is in need of continual supplies of water, for the sustenance of the animal and vegetable kingdoms, the processes by which these supplies are rendered available for such important purposes, form no inconsiderable part of the beautiful and connected mechanisms of the terraqueous Globe.
The great Instrument of communication between the surface of the Sea, and that of3the Land, is the Atmosphere, by means of which a perpetual supply of fresh water is derived from an Ocean of salt water, through the simple process of evaporation.
By this process, water is incessantly ascending in the state of Vapour, and again descending in the form of Dew and Rain.
Of the water thus supplied to the surface of the land, a small portion only returns to the Sea directly in seasons of flood through the channels of Rivers;[1]
A second portion is re-absorbed into the Atmosphere by Evaporation;
A third portion enters into the composition of Animal and Vegetable bodies;
A fourth portion descends into the strata, and is accumulated in their interstices into subterraneous sheets and reservoirs of water, from which it is discharged gradually at the surface in the form of perennial Springs, that form the ordinary supply of Rivers.
As soon as Springs issue from the Earth, their waters commence their return towards the Sea; rills unite into streamlets, which, by further accumulation form rivulets and rivers, and at length terminate in estuaries, where they mix again with their parent ocean. Here they remain, bearing part in all its various functions, until they are again evaporated into the Atmosphere, to pass and repass through the same Cycles of perpetual circulation.
The adaptations of the Atmosphere to this important service in the economy of the Globe belong not to the province of the geologist. Our task is limited to the consideration of the mechanical arrangements in the solid materials of the Earth, by means of which they co-operate with the Atmosphere, in administering to the circulation of the most important of all fluids.
There are two circumstances in the condition of the strata, which exert a material influence in collecting subterraneous stores of water, from which constant supplies are regularly giving forth in the form of springs; the first consists in the Alternation of porous beds of sand and stone, with strata of clay that are impermeable by water;[2] the second circumstance is the Dislocation of these strata, resulting from Fractures and Faults.
The simplest condition under which water is collected within the Earth, is in superficial beds of Gravel which rest on a sub-stratum of any kind of Clay. The Rain that falls upon a bed of gravel sinks down through the interstices of the gravel, and charges its lowest region with a subterraneous sheet of water, which is easily penetrated by wells, that seldom fail except in seasons of extreme drought. The accumulations of this water are relieved by Springs, overflowing from the lower margin of each bed of gravel.
A similar result takes place in almost all kinds of permeable strata, which have beneath them a bed of clay, or of any other impermeable material. The Rain water descends and accumulates in the lower region of each porous stratum next above the clay, and overflows in the same manner by perennial springs. Hence the numerous alternations of porous beds with beds impenetrable to water, that occur throughout the entire series of stratified rocks, produce effects of the highest consequence in the hydraulic condition of the Earth, and maintain a universal system of natural Reservoirs, from which water overflows incessantly in the form of Springs, that carry with them fertility into the adjacent valleys. (See Pl. 67, fig. 1, 8.)
The discharges of water from these reservoirs are much facilitated, and increased in number, by the occurrence of Faults or Fractures that intersect the strata.[3]
There are two systems of Springs which have their origin in Faults, the one supplied by water descending from the higher regions of strata adjacent to a fault, by which it is simply intercepted in its descent, find diverted to the surface in the form of perennial springs; (see Pl. 67, fig. 1, H.) the other maintained by water ascending from below by Hydrostatic pressure, (as in Artesian Wells,) and derived from strata, which at their contact with the fault, are often at a great depth; the water is conducted to this depth either by percolation through pores and crevices, or by small subterraneous channels in these strata, from more elevated distant regions, whence it descends, until its progress is arrested by the Fault. (See Pl. 67. Fig. 2, d, and Pl. 69. Fig. 2, H. L.)
Besides the advantages that arise to the whole of the Animal Creation, from these dispositions in the structure of the Earth, whereby natural supplies of water are multiplied almost to infinity over its surface, a further result, of vast and peculiar importance to Man, consists in the facilities which are afforded him of procuring artificial wells, throughout those parts of the world which are best adapted for human habitation.
The Causes of the rise of water in ordinary artificial wells, are the same that regulate its discharge from the natural apertures which give origin to springs; and as both these effects will be most intelligibly exemplified, by a consideration of the causes of the remarkable ascent of water to the surface, and often above the surface, in those peculiar perforations which are called Artesian Wells, our attention may here be profitably directed to their history.
Artesian Wells.
The name of Artesian Wells is applied to perpetually
flowing artificial fountains, obtained by boring a small hole,
through strata that are destitute of water, into lower strata
loaded with subterraneous sheets of this important fluid,
which ascends by hydrostatic pressure, through pipes let
down to conduct it to the surface. The name is derived
from Artois (the ancient Artesium,) where the practice of
making such wells has for a long time extensively prevailed.[4]
Artesian Wells are most available, and of the greatest use, in low and level districts where water cannot be obtained from superficial springs, or by ordinary wells of moderate depth. Fountains of this kind are known by the name of Blow wells, on the Eastern coast of Lincolnshire, in the low district covered by clay between the Wolds of Chalk near Louth, and the Sea-shore. These districts were without any springs, until it was discovered that by boring through this clay to the subjacent Chalk, a fountain might be obtained, which would flow incessantly to the height of several feet above the surface.
In the King's well at Sheerness sunk in 1781 through the London clay, into sandy strata of the Plastic clay formation, to the depth of 330 feet, the water rushed up violently from the bottom, and rose within eight feet of the surface. See Phil. Trans. 1784.) In the years 1828 and 1829 two more perfect Artesian wells were sunk nearly to the same depth in the Dock yards at Portsmouth and Gosport.
Wells of this kind have now become frequent in the neighbourhood of London, where perpetual Fountains are in some places obtained by deep perforations through the London clay, into porous beds of the Plastic clay formation, or into the Chalk.[5]
Important treatises upon the subject of Artesian Wells have lately been published by M. Héricart de Thury and M. Arago in France, and by M. Von Bruckmann in Germany.[6] 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,[7] and will afford abundant supplies of water for agricultural and domestic purposes and sometimes even for moving machinery. The quantity of water thus obtained in Artois is often sufficient to turn the wheels of Corn-mills.
In the Tertiary basin of Perpignan and the chalk of Tours, there are almost subterranean rivers having enormous upward pressure. The Water of an Artesian well in Roussillon rises from 30 to 50 feet above the surface. At Perpignan and Tours, M. Arago states that the water rushes up with so much force, that a Cannon-ball placed in the Pipe of an Artesian Well is violently ejected by the ascending stream.
In some places application has been made to economical purposes, of the higher temperature of the water rising from great depths. In Wurtemberg Von Bruckmann has applied the warm water of Artesian wells to heat a paper manufactory at Heilbronn, and to prevent the freezing of common water around his mill wheels. The same practice is also adopted in Alsace, and at Canstadt near Stuttgard. It has even been proposed to apply the heat of ascending springs to the warming of green houses. Artesian wells have long been used in Italy, in the duchy of Modena; they have also been successfully applied in Holland, China,[8] and N. America. By means of similar wells, it is probable that water may be raised to the surface of many parts of the sandy deserts of Africa and Asia, and it has been in contemplation to construct a series of these wells along the main road which crosses the Isthmus of Suez.
I have felt it important thus to enter into the theory of Artesian Wells, because their more frequent adoption will add to the facilities of supplying fresh Water in many regions of the Earth, particularly in low and level districts, where this prime necessary of Life is inaccessible by any other means; and because the theory of their mode of operation explains one of the most important and most common contrivances in the subterraneous economy of the Globe, for the production of natural springs.
By these compound results of the original disposition of the strata and their subsequent disturbances, the entire Crust of the Earth has become one grand and connected Apparatus of Hydraulic Machinery, co-operating incessantly with the Sea and with the Atmosphere, to dispense unfailing supplies of fresh Water over the habitable surface of the Land.[9]
Among the incidental advantages arising to Man from the introduction of Faults and Dislocations of the strata, into the system of curious arrangements that pervade the subterranean economy of the Globe, we may further include the circumstance that these fractures are the most frequent channels of issue to mineral and thermal waters, whose medicinal virtues alleviate many of the diseases of the Human Frame.[10]
Thus in the whole machinery of springs and Rivers, and the apparatus that is kept in action for their duration, through the instrumentality of a system of curiously constructed hills and valleys, receiving their supply occasionally from the rains of heaven, and treasuring it up in their everlasting storehouses to be dispensed perpetually by thousands of never-failing fountains, we see a provision not less striking, than it is important. So also in the adjustment of t-he relative quantities of Sea and Land, in such due proportions as to supply the earth by constant evaporation, without diminishing the waters of the ocean; and in the appointment of the Atmosphere to be the vehicle of this wonderful and unceasing circulation; in thus separating these waters from their native salt, (which though of the highest utility to preserve the purity of the sea, renders them unfit for the support of terrestrial animals or vegetables,) and transmitting them in genial showers to scatter fertility over the earth, and maintain the never-failing reservoirs of those springs and rivers by which they are again returned to mix with their parent ocean; in all these circumstances we find such evidence of nicely balanced adaptation of means to ends, of wise foresight, and benevolent intention, and infinite power, that he must be blind indeed, who refuses to recognize in them proofs of the most exalted attributes of the Creator."[11]
- ↑ It is stated by M. Arago, that one third only of the water which falls in rain, within the basin of the Seine, flows by that river into the sea: the remaining two thirds either return into the atmosphere by evaporation, or go to the support of vegetable and animal life, or find their way into the sea by subterraneous passages. Annuaire, pour l'An 1835.
- ↑ See p. 62.
- ↑ Mr. Townsend, in his Chapter on Springs, states, that there are six distinct systems of springs in the neighbourhood of Bath, which issue from as many regular strata of subterraneous water, formed by filtration through either sand or porous rocks, and placed each upon its subjacent bed of clay. From these, one system of springs is produced by overflowing in the direction towards which the strata are inclined, or have their dip; whilst another system results from the dislocation of the strata, and breaks out laterally through the fractures by which they are intersected.
It is stated by Mr. Hopkins, (Phil. Mag. Aug. 1834, p. 131,) that all the great springs in the Limestone District of Derbyshire are found in conjunction with great Faults, "I do not recollect (says he) a single exception to this rule, for I believe in every instance where I observed a powerful spring, I had independent evidence of the existence of a great fault."
- ↑ The manner of action of an Artesian Well is explained by the Section Pl. 69. Fig. 3, copied from M. Hericart de Thury's representation of a double Fountain at St. Ouen, which brings up water, from two water bearing strata at different levels below the surface. In this double fountain, the ascending forces of the water in the two strata A and B are different; the water from the lowest stratum B rising to the highest level A; that from the upper stratum A rising only to a'. The water from both strata is thus brought to the surface by one Bore Hole of sufficient size to contain a double pipe, viz. a smaller pipe included within a larger one, with an interval between them for the passage of water; thus, the smaller pipe b brings up the water of the lower stratum B, to the highest level of the fountain b″, whilst the larger pipe a brings up the water from stratum A to the lower level a: both these streams are employed to supply the Canal-basin at St. Ouen, above the level of the Seine. Should the lower stratum B contain pure water, and that in the upper stratum A be tainted, the pure water might by this apparatus be brought to the surface through the impure, without contact or contamination.
In common cases of Artesian wells, where a single pipe alone is used, if the Boring penetrates a bed containing impure water; it is continued deeper until it arrives at another stratum containing pure water; the bottom of the pipe being plunged into this pure water, it ascends within it, and is conducted to the surface through whatever impurities may exist in the superior strata. The impure water, through which the boring may pass in its descent, being excluded by the pipe from mixing with the pure water ascending from below.
- ↑ One of the first Artesian wells near London was that of Norland House on the N. W. of Holland House, made in 1794, and described in Phil. Trans. London, 1797. The water of this well was derived from sandy strata of the plastic clay formation, but so much obstruction by sand attends the admission of water to the pipes from this formation, that it is now generally found more convenient to pass lower through these sandy strata, and obtain water from the subjacent chalk. Examples of wells that rise to the surface of the lowest tract of land on the W. of London may be seen in the Artesian fountain in front of the Episcopal palace at Fulham, and in the garden of the Horticultural Society. Many such fountains have been made in the Town of Brentford, from which the water rises to the height of a few feet above the surface.
This height is found to diminish as the number of perpetually flowing fountains increases; and a general application of them would discharge the subjacent water so much more rapidly than it arrives through the interstices of the chalk, that fountains of this kind when numerous would cease to overflow, although the water within them would rise and maintain its level nearly at the surface of the land.
The Section, Pl. 68 is intended to explain the cause of the rise of water in Artesian Wells in the Basin of London, from permeable strata in the Plastic-clay formation, and subjacent Chalk. The water in all these strata is derived from the rain, which falls on those portions of their surface that are not covered by the London Clay, and is upheld by clay beds of the Gault, beneath the Chalk and Fire-stone. Thus admitted and sustained, it accumulates in the joints and crevices of these strata to the line A. B. at which it overflows by springs, in valleys, such as that represented in our section under C. Below this line, all the permeable strata must be permanently filled with a subterranean sheet of water, except where faults and other disturbing causes afford local sources of relief. Where these reliefs do not interfere, the horizontal line A, B, represents the level to which water would rise by hydrostatic pressure, in any perforations through the London Clay, either into sandy beds of the Plastic-clay formation, or into the Chalk; such as those represented at D. E. F. G. H. I. If the Perforation be made at G. or H. where the surface of the country is below the line A. B. the water will rise in a perpetually flowing Artesian fountain, as it does in the valley of the Thames between Brentford and London.
- ↑ See Héricart de Thury's Considerations sur la cause du Jaillissement des Eaux des puits forés, 1829.
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.
- ↑ An economical and easy method of sinking Artesian Wells and boring for coal, &c, has recently been practised near Saarbrück, by M. Sellow. Instead of the tardy and costly process of boring' with a number of Iron Rods screwed to each other, one heavy Bar of cast Iron about six feet long and four inches in diameter, armed at its lower end with a cutting Chisel, and surrounded by a hollow chamber, to receive through valves, and bring, up the detritus of the perforated stratum, is suspended from the end of a strong rope, which passes over a wheel or pulley fixed above the spot in which the hole is made. As this rope is raised up and down over the wheel, its tortion gives to the Bar of Iron a circular motion, sufficient to vary the place of the cutting Chisel at each descent. When the chamber is full, the whole apparatus is raised quickly to the surface to be unloaded, and is again let down by the action of the same wheel. This process has been long practised in China, from whence the report of its use has been brought to Europe. The Chinese are said to have bored in this manner to the depth of 1000 feet. M. Sellow has with this instrument lately made perforations 18 inches in diameter, and several hundred feet deep, for the purpose of ventilating coal mines at Saarbrïck. The general substitution of this method for the costly process of boring with rods of iron, may be of much public importance, especially where water can only be obtained from great depths.
- ↑ The causes of intermitting Springs, and ebbing and flowing wells, and many, minor irregularities in the Hydraulic Action of natural vents of water, depend on local Accidents, such as the interposition of Syphons, Cavities, &c., which are scarcely of sufficient importance to be noticed, in the general view we are here taking of the Causes of the Origin of Springs.
- ↑ Dr. Daubeny has shown that a large proportion of the thermal springs with which we are acquainted, arise through fractures situated on the great lines of dislocation of the strata. See Daubeny on Thermal Springs, Edin. Phil. Jour. April, 1832, p. 49. Professor Hoffmann has given examples of these fractures in the axis of valleys of elevation, through which chalybeate waters rise at Pyrmont, and in other valleys of Westphalia. See Pl. 67, fig, 2.
- ↑ Buckland, Inaug. Lecture, p. 13.