Theory of the Earth Volume Ii Part 9

It is not to _common_ observation that it belongs to see the effects of time, and the operation of physical causes, in what is to be perceived upon the surface of this earth; the shepherd thinks the mountain, on which he feeds his flock, to have been always there, or since the beginning of things; the inhabitant of the valley cultivates the soil as his father had done, and thinks that this soil is coeval with the valley or the mountain. But the man of scientific observation, who looks into the chain of physical events connected with the present state of things, sees great changes that have been made, and foresees a different state that must follow in time, from the continued operation of that which actually is in nature.

It is thus that enlightened natural history affords to philosophy principles, from whence the most important conclusions may be drawn.

It is thus that a system may be perceived in that which, to common observation, seems to be nothing but the disorderly accident of things; a system in which wisdom and benevolence conduct the endless order of a changing world. What a comfort to man, for whom that system was contrived, as the only living being on this earth who can perceive it; what a comfort, I say, to think that the Author of our existence has given such evident marks of his good-will towards man, in this progressive state of his understanding! What greater security can be desired for the continuance of our intellectual existence,--an existence which rises infinitely above that of the mere animal, conducted by reason for the purposes of life alone.

The view of this interesting subject, which I had given in the first part, published in the Transactions of the Edinburgh Royal Society, has been seen by some men of science in a light which does not allow them, it would appear, to admit of the general principle which I would thereby endeavour to establish. Some contend that the rivers do not travel the material of the decaying land;--Why?--because they have not seen all those materials moved. Others alledge, that stones and rocks may be formed upon the surface of the earth, instead of being there all in a state of decay. These are matters of fact which it is in the power of men who have proper observation to determine; it is my business to generalise those facts and observations, and to bring them in confirmation of a theory which is necessarily founded upon the decaying nature and perishing state of all that appears to us above the surface of the sea.

Nothing is more evident, than that the general effect of mineral operations is to consolidate that which had been in an incoherent state when formed at the bottom of the sea, and thus to produce those rocks and indurated bodies which const.i.tute the basis of our vegetable soil; but, that indurating or consolidating operation is not the immediate object of our observation; and, to see the evidence of that operation, or the nature of that cause, requires a long chain of reasoning from the most extensive physical principles. Our present subject of investigation requires no such abstract distant _media_, by which the effect is to be connected with its cause; the actual operation in general is the object of our immediate observation; and here we have only to reason from less to more, and not to h.o.m.ologate things which may, to men of narrow principles, appear to be of different kinds. But even here we find difficulty in persuading those who have taken unjust views of things; for, those who will not deny the truth of every step in this chain of reasoning, will deny the end to which it leads, merely because they are not disposed to admit the progress of that order which appears in nature.

In the last chapter, I have been using arguments to prove that M. de Luc has reasoned erroneously, in concluding the future stability of a continent; and I have been endeavouring to show that our continent is necessarily wasted in procuring food to plants, or in serving the various purposes of a system of living animals. We have now in view to ill.u.s.trate this theory of the degradation of the surface of the earth; a theory necessarily leading to that system of the world in which a provision is made for future continents; and a theory explaining various natural appearances which otherwise are not to be understood. A door may thus be opened for the investigation of natural history, particularly that which traces back, from the present state of things, those operations of nature which are more immediately connected with what we take much pleasure to behold, viz. the surface of the earth stored with such a variety of beautiful plants, and inhabited by such a diversity of animals, all subservient to the use of man.

There are two ways in which we may look for the transactions of time past, in the present state of things, upon the surface of this earth, and read the operations of an ancient date in those which are daily transacted under our eye. The one of these is to examine the soil, and to trace the origin of that which we find loose upon the surface of the earth, or only compacted by the soft and cohesive nature of some of its materials. In thus studying the soil we shall learn the destruction of the solid parts; and though, by this means, we cannot form an estimate of the quant.i.ty of this destruction which had been made, we shall, upon many occasions, see a certain _minimum_ of this quant.i.ty which may perhaps astonish us.

The second method here proposed, is to examine the solid part of the earth, in order to learn the quant.i.ty of matter which had been separated from this ma.s.s. Here also we shall not be able to compute the quant.i.ty of what had been destroyed; but we shall every where find a certain _minimum_ of this quant.i.ty, which will give us an extensive view with regard to the operation of the elements and seasons upon the surface of this earth. We shall now examine more particularly those two ways of judging with regard to the operations of time past, and the changes which have been made upon the surface of our land, by those active causes, which, being in the const.i.tution of this earth, must continue to operate with undiminished power, and tend to preserve the _whole_ amidst the destruction of its particular parts.

The quality of the soil or travelled earth of the globe is various; because the solid parts, from the destruction of which the soil is formed, consist of very different substances, in the different portions of each country. Thus, in one part of a country, the soil will be calcareous, or containing much of that species of substance; in another, again, it will be argillaceous; in another sandy, where the prevailing substance is siliceous. These are the original soils; other substances may be considered as advent.i.tious to this soil, though natural to the surface of the earth, which is covered with plants and animals. The substance of those animal and vegetable bodies, mixed with the soil, adds greater fertility to the earth, and gives a soil which is still more compounded in its nature, but still composed of those materials now enumerated.

We have been now supposing the solid parts below, or in the same field, as furnishing materials of which the soil is formed; this soil then partakes of the nature of those solid parts, whether more simple or more compound. There is, however, another subject of variety, or still greater composition in soils; this is the transportation of materials from a distance; and this, in general, is performed by the ablution of water, in following the declivity of the surface. But sand is sometimes travelled by the wind, and proceeds along the surface of the earth, without regard to the declivity, and changes the nature of soil in those places which happen to be exposed to this accident.

There cannot be any extensive, great, or distant travelling of sand or soil by means of the wind, except in those places which are sterile for want of rain, and thus are dest.i.tute of rivers and of streams; for, these running waters form every where a bar to this progressive movement of the soil, even if the sterility or dryness should permit the blowing of the sand. But the operation of streams and rivers, carrying soil and stones along the surface of the earth, is constant, great, and general over all the globe, so far as a superfluity of water, in the seasons of rain, falls upon the earth.

From the amazing quant.i.ty of those far travelled materials, which in many places are found upon the surface of the ground, we may with certainty conclude, that there has been a great consumption of the most hard and solid parts of the land; and therefore that there must necessarily have been a still much greater destruction of the more soft and tender substances, and the more light and subtile parts which, during those operations of water, had been floated away into the sea.

This appears from the enormous quant.i.ties of stones and gravel which have been transported at distances that seem incredible, and deposited at heights above the present rivers, which renders the conveyance of those bodies altogether inconceivable by any natural operation, or impossible from the present shape of the surface. This therefore leads us to conclude, that the surface of the earth must have been greatly changed since the time of those deposits of certain foreign materials of the soil. Examples of this kind have been already given. I shall now give one from the Journal de Physique.

Les bords du Rhone aux environs de Lyon, et sur la longueur de quarante lieues, et de plus, des montagnes entieres, dans le meme pays, sont formes de pierres dont on ne trouve les a.n.a.logues que dans la Suisse. Ce fait presqu'incomprehensible est accompagne de beaucoup de circonstances qui meritent d'etre detaillees dans un discours plus longue que celui-ci. Il y a cependant une que je ne peux pas m'empecher de rapporter ici, comme une suite de ce que je viens de dire.

Dans cette grand catastrophe, a laquelle j'attribue le transport de ces matieres alpines, il se fit de grandes echancrures dans le Jura; les plus profondes que j'aie vues sont celles de Jougue de Sainte-Croix, du val de Mousthier Travers, de Someboz au val de Saint-Inver, une cinquieme aux environs du village de Grange, trois lieues plus bas que Bienne, et une sixieme a quatre a cinq lieues plus bas que Soleure, a l'endroit dit la cluse. Cette derniere est la plus profonde, et se trouve de niveau avec les eaux de l'Aar. Beaucoup de ces matieres etrangeres au Jura, ont pa.s.se par ces echancrures, et sans doute, par bien d'autres et se sont repandues, dans plusieurs de ces vallees. J'en ai vu un suite bien marquee qui a pa.s.se par Jougue, par Saint-Antoine, part Mont Perreux, les Grangettes, les Granges Friards, Oye, et qui est allee jusqu'aux plaines de Pontarlier. Cette suite est en ligne droite vis-a vis l'echancrure de Jougue, et la direction de la vallee qui est au bas de ce village. On en trouve quelques morceaux a Metabiefs, mais je n'en ai point vu aux Longevilles, ni a Roche-Jean. Il y en a au-dessus de Saint-Croix ou d'autres ont pu pa.s.ser aussi pour aller de meme aux environs de Portarlier. Il y en a dans le val de Mousthier-Travers jusqu'au dessus de village de b.u.t.te; elles ont meme pa.s.se les roches de Saint-Sulpice du cote des Verrieres de Suisse, ou l'on a ete oblige d'en faire sauter de gros blocs avec de la poudre pour degager la grande route; il y en a dans les vallees de Tavannes, et de Delemont; on en trouve bien plus loin, j'en ai vu pres de Roulans, et je ne douterois pas que les pierres meulieres de Moissez et des environs n'eussent la meme origine.

M. de Saussure, who has so well observed every thing that can be perceived upon the surface of the earth, gives us the following remarks which are general to mountainous countries. (Voyages dans les Alpes, tome 2d -- 717).

Dans le haut des vallees entourees de hautes montagnes, on ne voit point de cailloux roulees, qui soient etrangers a la vallee meme dans laquelle on les trouve; ceux que l'on y rencontre ne sont jamais que les debris des montagnes voisines. Dans le plaines au contraire, et a l'embouchure des vallees, qui aboutissent aux plaines et meme a.s.sez haut sur les pentes des montagnes qui bordent ces plaines, on trouve des cailloux et des blocs que l'on diroit tombes du ciel, tant leur nature differe de toute ce que l'on voit dans les environs.

Here are facts which can only be explained in supposing that the valleys have been hollowed out of the solid ma.s.s, by the gradual operation of the rivers. In that case stones, travelled from a far, will be found at considerable heights, upon the sides of the valleys at their under end, or where, as our author says, they terminate in plains.

We have a striking example of the operation of time and the influences of the atmosphere, in wasting the surface of the rocks, and forming soil upon the earth; this is the kaolin of the Chinese, or the true porcelain earth, which is the produce of granite countries. The feldspar of the granite rock exposed to the atmosphere is corroded very slowly indeed, by the effects of air and moisture, and in having the soluble earth or calcareous part of its composition dissolved; the surface of this stone, thus, in a long course of time, becomes opaque in having the white siliceous earth exposed to view, and thus appears like a calcined substance. The snows and rain detaches from this surface of the rock the white earth, which being deposited in the plain below, forms a stratum of kaolin more or less pure, according to the circ.u.mstance of the place.

As this operation of the atmosphere upon the surface of granite is so extremely slow as to be altogether unmeasurable to man; and as there are in many places of the earth inexhaustible quant.i.ties of this kaolin, notwithstanding a small portion only of the ablution of the rock had been retained upon the surface and deposited by itself, it must appear that much time had been required for ama.s.sing those beds of kaolin, and that these operations, which in the age of a continent is nothing, or only as a day, are, with regard to the experience of man, unmeasurable.

For approbation of this theory, it is not necessary to show, that wherever there is granite found, there should be also kaolin observed; but it is necessary that wherever kaolin is found, there should be also granite or feldspar to explain its origin; and to this proof the theory is most willingly submitted. The following are the places which have come to my knowledge. First Loch Dune in the shire of Ayr; this lake receives its water from the granite hills which are at its head.

Secondly, some small lakes which receive the washings of the granite mountain, Crifle, in East Galloway. Thirdly, Cornwall, a county in which I have not been, but which is sufficiently known as possessing kaolin and granite.

Another example from a very distant country we have both from M.

Pallas, in the Oural mountains, and from M. Patrin, who has given a mineralogical _notice_ of the Douari, _Journal de physique, Mars_ 1791.

Here we find the following observation.

Parmi les chose interessantes qu'offrent les rives de Chilea, on remarque au dessous de la fonderie, des collines de petunt-fe blanc comme la neige, pa.r.s.eme de mica argentin de la plus grande tenuite.

Dans le voisinage de ce petunt-fe est une argile micacee, qui en est peut-etre une decomposition: on essaya en ma presence d'en faire de la poterie qui avoit tous les caracteres du meilleurs biscuit de porcelaine.

We have now been endeavouring to ill.u.s.trate the wasting and washing away of the solid land, in the examples of decayed rocks and water worn stones, all of which are traceable, though at a great distance, to their source; we are now to consider another species of substance, which is still more particular as to the place of its production, or to its original situation, this being only in the veins of the earth. Among all the various productions of mineral veins, we have only now in view some particular metallic substances which do not seem to waste and be dissolved, as many of them are, in being long exposed to the influence of air and rain. When, therefore, the solid parts of the land are wasted in time, and carried away from the surface of the earth, the contents of the veins, which are occasionally found in those decayed parts of the land, are also carried away in the stream; but as the specific gravity of those metallic contents is much greater than the other stony materials moved in the stream, they sink to the bottom, and tend much more to be deposited upon the land, than those stones which had moved with them from their place. Hence it is, that deposits, rich in those metallic substances, are formed in certain places of the soil; and these are sought for, upon account of the value of their contents. Thus, stream tin, which in the time of the Romans formed a subject of traffic, is still found in the soil of Cornwall, even in great profusion, at this day.

Nothing can tend more to ill.u.s.trate this travelling of the wasted surface of the solid land, than the contents of those mineral veins suffering in the general destruction of things, but partly saved from that total ablution by which so much of the solid parts had been made to disappear; and nothing can, in a more beautiful manner, show this order of things, than the method practised by the Cornish miners in quest of the original country of that metal, by _shoding_, (as it is called) upwards in running back the tract in which the stream tin had been conveyed. This is done by trying parcels of the soil, in always mounting to see from whence the mineral below had come.

Gold is thus found almost in every country but it is only in the most sparing manner that it may thus be in general procured, by reason of the few veins in which gold is found, and the small quant.i.ty of this metal contained in those veins. America, however, affords an example of veins rich in gold, and it is also there that quant.i.ties of stream gold is found in the soil, bearing a due proportion to the number and riches of the veins.

I shall give an example concerning the situation in which this stream gold is found in Peru (Voyage au Perou, par M. Bouguer, page 49.)

Cette Cordeliere occidentale contient beaucoup d'or de meme que le pied de l'orient, et celui d'une autres chaine tres-longue qui s'en detache un peu au sud de Popayan, et qui apres avoir pa.s.se par Santa Fe de Bogota, et par Merida, va se terminer vers Caracas sur la mer du nord; outre que l'or en paillettes occupe toujours des postes a.s.sez bas a l'egard du reste de la Cordeliere, on ne peut aussi jamais le decouvrir qu'en enlevant presque toujours deux couches de differentes terres qui le cachent. La premiere, qui est de la terre ordinaire, a trois ou quatre pieds d'epaisseur et quelquefois dix ou douze. On trouve souvent au dessous une couche moins epaisse qui tire sur le jaune, et plus bas est une troisieme qui a une couleur violette, qui a souvent trois ou quatre pieds d'epaisseur, mais qui n'a aussi quelquefois qu'un pouce, et c'est cette troisieme dans laquelle l'or est mele. Au dessous la terre change encore de couleur, elle devient noire comme a la surface du sol, et elle ne contient aucun metal. D'ailleurs on ne creuse pas indistinctement par tout. On se determine a chercher en certains endroits plutot qu'en d'autres par la pente de terrain. On agit comme si l'or avant que d'avoir ete couvert par les deux couches superieures, avoit ete charrie par des eaux courantes. On s'est a.s.sure aussi que les terres une fois _lavees_ ou depouillee de leurs richesses n'en produisent point d'autres; ce qui prouve que l'or y avoit ete comme depose.

Therefore, whether we consider the quant.i.ty or the quality of the materials which are found composing the soil upon the surface of the earth, we must be led to acknowledge an immense waste of the solid parts, in procuring those relicts which indicate what had been destroyed.

We have now to examine what is left of that solid part which had furnished the materials of our soil; this is the part which supports the vegetable or travelled earth, and this earth sustains the plants and animals which live upon the globe. It is by this solid part that we are to judge concerning the operations of time past; of those destructive operations by which so great a portion of the earth had been wasted and carried away, and is now sunk at the bottom of the sea.

Man first sees things upon the surface of the earth no otherwise than the brute, who is made to act according to the mere impulse of his sense and reason, without inquiring into what had been the former state of things, or what will be the future. But man does not continue in that state of ignorance or insensibility to truth; and there are few of those who have the opportunity of enlightening their minds with intellectual knowledge, that do not wish at some time or another to be informed of what concerns the whole, and to look into the transactions of time past, as well as to form some judgment with regard to future events.

It is only from the examination of the present state of things that judgments may be formed, in just reasoning, concerning what had been transacted in a former period of time; and it is only by seeing what had been the regular course of things, that any knowledge can be formed of what is afterwards to happen; but, having observed with accuracy the matter of fact, and having thus reasoned as we ought, without supposition or misinformation, the result will be no more precarious than any other subject of human understanding. To those who thus exercise their minds, the following remarks may furnish a subject for some speculation. Now, though to human policy it imports not any thing, perhaps, to know what alterations time had made upon the form and quant.i.ty of this earth, divided into kingdoms, states, or empires, or what may become of this continent long after every kingdom now subsisting is forgotten, it much concerns the present happiness of man to know himself, to see the wisdom of that system which we ascribe to nature, and to understand the beauty and utility of those objects which he sees.

There are two different operations belonging to the surface of this globe which we are now to consider, and by which we shall be enabled to form some computation of what had been in s.p.a.ce and time, from that which now appears. Moving water is the means employed in both those operations; but, in the one case, it is the water of the sea; in the other again, it is the water of the land. The effect of the one operation is the wasting of the coast, and the diminution of that basis on which our land and soil depends; of the other, again, it is the degradation of our mountains, and the wasting of our soil. In the course of this last operation, there is also occasionally land formed in the sea, in addition to our coast.

With regard to the wearing of the coast by the agitation of the waves, this is an operation of which some understanding is to be formed from the surest of all records, from a careful examination of our sh.o.r.es which are in this decaying state, and by observing what has been removed from those portions which we find remaining. Few people have either the skill or the opportunity of thus judging of the state of our earth from that which actually appears; but there is no person, who studies this science of geology, that may not satisfy himself with regard to the truth of this theory, by looking into our maps and charts, and making proper allowances for causes which cannot appear in the maps, but which may be understood by a person of knowledge making observations on the spot. In order to a.s.sist this study, the following observations may be made.

It is a general observation among mariners, that a high coast and rocky sh.o.r.e have deep water; whereas a low coast, and sandy sh.o.r.e, are as naturally attended with shallow water. The explanation of this fact will appear by considering, that a steep rocky coast is occasioned by the sea having worn away the land; and, when that is the case, we are not to expect sand should be acc.u.mulated upon that sh.o.r.e, so as to make the sea shallow. Look round all the coasts of Great Britain and Ireland that are exposed to the wide ocean, as likewise those of France and Norway, deep water, and a worn coast, are universally to be acknowledged. If again the coast is shallow, this is a proof that the land affords more materials than the sea can carry away; consequently, instead of being impaired, the coast may here increase and be protruded from the land.

Such is the case in many places along the coast of North America, where several reasons concur in acc.u.mulating sand upon that coast; for, not only is the sh.o.r.e plentifully provided with sand from the rivers of that continent, but also the sand of the Mexican Gulf would appear to be carried along this coast with the stream which flows here towards the north, and which has thus contributed to form the banks of Newfoundland.

The second general observation is to be considered as respecting the shape of coasts, in like manner as the first had in view their elevations. Now, it is plain that the shape of the coast, in any part of the land, must depend upon a combination of two different causes. The first of these is the composition of the land or solid parts of the coast; if this be uniform and regular, so will be the shape of the coast; if it is irregular and mixed, consisting of parts of very different degrees of hardness and resistance to the wasting operations, the coast will then be, _cet. par._ irregular and indented. The second, again, respects the wearing power. If this wearing power shall be supposed to be equally applied to all the coast; and, if every part of that coast were of an equal quality or resisting power, no explanation could be given, from the present state of things, for the particular shape of that coast, which ought then to be wasted in an equable manner by the sea. But neither is the coast, of any extensive country at least, composed of such uniform materials; nor is the application of the wearing power to the coast an equal thing; and this will form the subject of another observation. The third general observation, therefore, regards the operations of the sea upon the coast, and the effects which may be perceived in consequence of that cause, independent of the qualities of the coast, or supposing them in general to be alike.

Here, according to the theory, we should expect to find deep water and an indented coast upon a country, in proportion as that coast is exposed to the violence of the sea, or is open directly to the ocean. We have but to look along the west coast of Norway, the north-west of Scotland, the west of Ireland, and the south-west of England and of France; and we shall soon be convinced that the sea has made ravages upon those coasts in proportion to its power, and has left them in a shape corresponding to the composition of the land, in destroying the softer, and leaving the harder parts[14].

[Footnote 14: M. de Lamblardie, _ingenieur des ponts et chaussees_, has made a calculation, seemingly upon good grounds, with regard to the wasting of a part of the coast of France, between the Seine and the Somme. This coast is composed of _falaises_, (or chalk cliffs, like the opposite coast of England), which are 200 feet high above the level of the sea, composed of strata of marl, separated by beds of flint. This coast is found to be wasted, at an average, at the rate of one foot _per annum_. We may thus perhaps form some idea of the time since the coast of France and that of England had been here united, or one continued ma.s.s of those strata which are the same on both those coasts.]

With those hard and rugged coasts of Britain and Ireland, let us contrast the east coasts; What a difference between these and the west side! Upon the west side, there are no sand banks left upon the coast; the mariner has nothing there to fear but rocks. It is otherwise on the east; here we find a tamer coast, and, in many places, a sandy bottom.

On the west, nothing appears opposed to the storm of the ocean except the hardest and most solid rock; on the east, we find coasts exposed to the sea which could not have remained in a similar situation on the west. Let us but compare the two opposite coasts of England, viz. the promontory of Norfolk and Suffolk upon the one side, and Pembrokeshire and Carnarvonshire on the other, both similarly exposed, the one to the north east storm of the German sea, the other to the south west billows of the Atlantic. What a striking difference! The coast in the bay of Cardigan is a hard and strong coast compared with that of Norfolk and Suffolk; the one is strong schistus, the other the most tender clay; yet the soft coast stands protuberant to the sea, the harder coast is hollowed out into a bay; the one has no protection but the sands with which it is surrounded, the other had not remained till this day but for the protection of the most solid rocks of Pembrokeshire and Carnarvonshire, which oppose the fury of the waves.

The last general observation which I shall propose, has, for its subject, a more enlarged view than those now taken of the coast, a view indeed which is not so immediately the object of our observation, but which is nevertheless to be made most evident, by means of the others now considered. We have seen that the land exposed to the sea is destroyed, and the coast wasted more or less, in proportion to the wearing causes, and to the different resisting powers opposed to those causes of decay; we are now to make our observations with regard to the extent and quality of that which has been already destroyed, a subject which can only be conjectured at from the scientific view which may be taken of things, and from the careful examination of that which has been left behind upon the different coasts.

Our land is wasted by the sea; and there is also a natural progress to be observed which necessarily takes place on this occasion; for, the coast is found variously indented, that is to say, more or less, according as the land is exposed to this wasting and wearing operation of the sea, and according as the wasted land is composed of parts resisting with different degrees of power the destroying cause. The land, thus being worn and wasted away, forms here and there peninsulas, which are the more durable portions of that which had been destroyed around; and these remaining portions are still connected with the main land, of which they at present form a part.

But those promontories and peninsulas are gradually detached from the main land, in thus forming islands, which are but little removed from the land. An example of this we have in Anglesay, which is but one degree removed from the state of being a promontory. These islands again, in being subdivided, are converted into barren rocks, which point out to us the course in which the lost or wasted land upon the coast had formerly existed.

To be satisfied of this, let us but look upon the western coast of Scotland; from the islands of St. Kilda to Galloway, on the one side, and to Shetland on the other; in this tract, we have every testimony, for the truth of the doctrine, that is consistent with the nature of the subject. The progress of things is too slow to admit of any evidence drawn immediately from observation; but every other proof is at hand; every appearance corresponds with the theory; and of every step in the progress, from a continent of high land to the point of a rock sunk below the surface of the sea, abundant examples may be found. We do not see the beginning and ending of any one island or piece of country, because the operation is only accomplished in the course of time, and the experience of man is only in the present moment. But man has science and reason, in order to understand what has already been from what appears; and we have but to open our eyes to see all the stages of the operation although not in one individual object. Now, where the nature of things will not admit of having all and every step of the progress to be perceived in one object, an indefinite progression in the various states of different objects, showing the series or gradation from a continent to a rock, must form a proof in which no deficiency will be found.

I have given for example the coast of Scotland; but all over the world where there is a coast not covered with sand, or where it is exposed to the violence of the sea, it is the same. Take the map of any country, provided it be sufficiently particular, and you will see the breaking of continents or islands, first, into promontories or peninsulas; secondly, into islands which stand on the same solid basis with the continent; and, lastly, into rocks which are related to the islands, in like manner as those parasitical islands are related to the head lands and the sh.o.r.e. Here is a general fact, from the simple inspection of which we must conclude one of two things; either that those rocks and smaller islands, which we have termed parasitical, are in a state of progression, by which in time they will be joined to the main land, and form one continent; or that they are in a state of degradation, by which in time they will be made to disappear. There is no other supposition to be made; and, of that alternative, there is no room to hesitate a moment which to choose. This is not a matter of mere probability, it is the subject of physical demonstration. Should we find an old ma.n.u.script in a similar condition, we could not conclude with more certainty, that the deficient or intervening places had been destroyed, than we here conclude that the part which is now wanting, between the two remaining portions of the same rock or strata, had once connected those two portions, and had been destroyed by the operation of those causes which are every day employed in still increasing the breach.

Though over all the world, where the sh.o.r.e is washed bare by the sea, examples are to be found which require but to be seen to give compleat conviction, it is not in every place that the eye of a naturalist has been employed in taking this view of the coast; nor is it upon every occasion that enlightened philosophers of this kind have given their thoughts upon the subject. M. de Spallanzani has given us the following observations with regard to the coast of Italy[15].

[Footnote 15: Observations sur la Physique, etc. Juliet 1786.]

Autant l'interieur du pet.i.t bourg de Porto-venere et les rochers qui l'environnent sont a l'abri des tempetes, autant les parties exterieures sont exposees aux coups de mer les plus violens, lorsqu'elles sont en proie au deux terribles vents d'Afrique et a celui du sud-est. Ce dernier en particulier souleve les flots avec tant de violence et a une telle hauteur contre les ecueils qui servent de defense a ce pet.i.t terrain, que la mer semble menacer de l'engloutir. J'ai ete le temoin d'un de ces orages, et quoique je fusse a l'abri de tout danger, je ne pourroit vous representer l'horreur que me fit eprouver ce spectacle.

J'ai voulu prendre avec exact.i.tude la hauteur moyenne de l'elevation des flots dans les plus violens coups de vent; et quand je vous en parlerai vous serez etonne de leur force et de l'etendue de leurs effets. Les rochers qui sont a la partie meridionale de Porto-venere se rongent et se detruisent peu-a-peu de meme que les trois isles voisines _Tiro_, le _pet.i.t Tiro_, et _Palmarin_. On le remarque surtout dans cette dernier: les bords voisins de la terre ont une pente douce; ils sont couverts d'arbres et de plantes, tandis que la partie opposee est deserte et inaccessible couverte de precipices, de ruines et d'horreurs; les autres parties du rivage sont renfermees par la riviere du ponent et par celle du levant, de meme que celles qui s'approchent des cotes de Provence. Il me paroit que la mer a beaucoup gagne sur le terre dans ces parages; et pour parler seulement de Palmarin, la plus grande, et la plus remarquable des trois isles que j'ai nommees, je crois etre suffisamment fonde pour conclure que la meme pente facile et longue qu'on observe du cote de la terre avoit aussi existe du cote de la mer; mais que cette derniere avoit ete detruite par les orages, qui se sont succedes pendant le cours de siecles. La vue reflechie de ces trois isles me force a les regarder comme ayant ete autre fois reunies, et formant une isle seule par leur reunion, ou plutot comme une presqu'ile attenante a Porto-Venere.

We have a still more interesting observation made upon this same coast of Italy, by a naturalist to whom the world is much indebted for his excellent remarks upon what he has, by his great industry, brought to light. I mean the Chevalier de Dolomieu; where-ever he goes, natural history reaps the benefit of the most enlightened observations. We are now to avail ourselves of his Memoire sur les Iles Ponces.