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:[ (return) ] M. de Lamblardie, ingénieur des ponts et chaussées, 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 mass 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 shore. 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 manuscript 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 shore 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:[ (return) ] Observations sur la Physique, etc. Juillet 1786.