mineral veins were charged with their precious contents; whether Segregation, or Sublimation, were the exclusive method by which the metals were accumulated; or, whether each of the supposed causes may have operated simultaneously or consecutively in their production; the existence of these veins remains a fact of the highest importance to the human race: and although the Disturbances, and other processes in which they originated, may have taken place at periods long antecedent to the creation of our species, we may reasonably infer, that a provision for the comfort and convenience of the last, and most perfect creatures He was about to place upon its surface, was in the providential contemplation of the Creator, in his primary disposal of the physical forces, which have caused some of the earliest, and most violent Perturbations of the globe.

That part of the History of Metals which relates to their various Properties and Uses, and their especial Adaptation to the Physical condition of Man, has been so ably and amply illustrated by two of my Associates in this Series of Treatises, that I have more satisfaction in referring my readers to the Chapters of Dr. Kidd and Dr. Prout upon these subjects than in attempting myself to follow the history of the productions of metallic veins, beyond the sources from which they are derived within the body of the Earth.

A summary of the all-important Uses of Metals to Mankind. is thus briefly given, by one of our earliest and most original writers on Physico-theology.

"As for Metals, they are so many ways useful to mankind, and those Uses so well known to all, that it would be lost labour

556

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.

to say anything of them: without the use of these we could have nothing of culture or civility: no Tillage or Agriculture; no Reaping or Mowing; no Ploughing or Digging; no Pruning or Loping; no Grafting or Insition; no mechanical Arts or Trades; no Vessels or Utensils of Household-stuff; no convenient Houses or Edifices; no Shipping or Navigation. What a kind of barbarous and sordid life we must necessarily have lived, the Indians in the Northern part of America are a clear demonstration. Only it is remarkable that those which are of most frequent and necessary use, as Iron, Brass and Lead, are the most common and plentiful: others that are more rare, may better be spared, yet are they thereby qualified to be made the common measure and standard of the value of all other commodities, and so to serve for Coin or Money, to which use they have been employed by all civil Nations in all Ages." Ray's Wisdom of God in the Creation. Pt. i. 5th ed. 1709, p. 110.

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 of the 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 ;*

A second portion is re-absorbed into the Atmosphere by Evaporation;

A third portion enters into the composition of Animal and Vegetable bodies;

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.

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,

ALTERNATIONS OF CLAY WITH PORous strata. 559

with strata of clay that are impermeable by water; 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 an universal system of natural Reservoirs, from which water

* See pp. 70, 71.