Coral rocks.

Where the shore is flat or shelving the coast of Sumatra, as of all other tropical islands, is defended from the attacks of the sea by a reef or ledge of coral rock on which the surfs exert their violence without further effect than that of keeping its surface even, and reducing to powder those beautiful excrescences and ramifications which have been so much the object of the naturalist’s curiosity, and which some ingenious men who have analysed them contend to be the work of insects.  The coral powder is in particular places accumulated on the shore in great quantities, and appears, when not closely inspected, like a fine white sand.

Surf.

The surf (a word not to be found, I believe, in our dictionaries) is used in India, and by navigators in general, to express a peculiar swell and breaking of the sea upon the shore; the phenomena of which not having been hitherto much adverted to by writers I shall be the more circumstantial in my description of them.

The surf forms sometimes but a single range along the shore.  At other times there is a succession of two, three, four, or more, behind each other, extending perhaps half a mile out to sea.  The number of ranges is generally in proportion to the height and violence of the surf.

The surf begins to assume its form at some distance from the place where it breaks, gradually accumulating as it moves forward till it gains a height, in common, of fifteen to twenty feet,* when it overhangs at top and falls like a cascade, nearly perpendicular, involving itself as it descends.  The noise made by the fall is prodigious, and during the stillness of the night may be heard many miles up the country.

(Footnote.  It may be presumed that in this estimation of its height I was considerably deceived.)

Though in the rising and formation of the surf the water seems to have a quick progressive motion towards the land, yet a light body on the surface is not carried forward, but, on the contrary, if the tide is ebbing, will recede from the shore; from which it would follow that the motion is only propagated in the water, like sound in air, and not the mass of water protruded.  A similar species of motion is observed on shaking at one end a long cord held moderately slack, which is expressed by the word undulation.  I have sometimes remarked however that a body which sinks deep and takes hold of the water appears to move towards shore with the course of the surf, as is perceptible in a boat landing which seems to shoot swiftly forward on the top of the swell; though probably it is only after having reached the summit, and may owe its velocity to its own weight in the descent.

Countries where the surfs prevail require boats of a peculiar construction, and the art of managing them demands the experience of a man’s life.  All European boats are more or less unfit, and seldom fail to occasion the sacrifice of the people on board them, in the imprudent attempts that are sometimes made to land with them on the open coast.  The natives of Coromandel are remarkably expert in the management of their craft; but it is to be observed that the intervals between the breaking of the surfs are usually on that coast much longer than on the coast of Sumatra.