In the county of Dumfries there are appearances of the same kind, as in the course of the Nith, in which we have the valleys of Sanquhar, Closeburn, and Dum fries; also in other parts of Scotland.
Similar appearances are to be observed in almost every quarter of the globe; and many of the lakes we see so abundantly distributed over the surface of the globe are to be considered as similar basins, but filled with water.
28. Having in the preceding sections described the various inequalities observable on that portion of the surface of the globe which is elevated above the level of the sea, we may now give a short description of the inequalities discoverable on the bottom of the era, or that part of the globe which is still covered with From the observations of mariners, we learn that the bottom of the sea has very considerable inequalities, and that these correspond, in many respects, to those observed on the surface of the land. Indeed this must be the case, when we consider that the present dry land was fornteily the bottom of the sea. In paragraph 6. we mentioned, that it does not present so great a va riety, or so beautiful a system of elevations and depres sions, as the dry land ; and this difference is also easily explained. The submarine land must be exposed, for many ages, to the action of the waves of the ocean, and of rain, rivers, and lakes, before its surface can agree, in all its features, with that of the dry land.
When the ground at the bottom of the sea approaches near to the surface of the water, and is pretty level, it is denominated a shoal. The Dogger Bank, in the North Sea, is an example of the shoal surface. It resembles the plains on the dry land ; it makes the transition from the dry land to the submarine, and will no doubt one day be changed into a plain. Deep submarine plains also often occur. Sometimes the bottom of the sea has a very uneven surface, and is composed of hills, either of sand and gravel, particularly near the coast, (as is the case on the coast of Holland), or of rocky hills, or of cliffs and other irregularities. The summits of these submarine hills form islands, and these sometimes ap pear as continuations of the high country on the dry land. We sometimes also meet with great hollows, which are unfathomable.
The coral reefs that surround the islands in the South Sea and Indian Ocean are to be viewed as a variety of the shoal surface already mentioned. These are the work of very minute animals. They occur in vest abundance along the east coast of New Holland, and in the South Sea, particularly to the eastward of the Friendly Islands, from the 10° to 15° South Latitude. A reel of this kind surrounds the island of Otaheite, and rises like a wall from unfathomable depths. Many of the other islands arc encompassed with similar reefs, in particular New Holland, New Caledonia, &c. Captain Flinders says, the quantity of coral reefs between New Holland and New Caledonia and New Guinea is such, that this might be called the coral sea. Thus for 350 miles, in a straight line from south-east to north-west, in the east coast of New Holland, is a coral reef uain tempted by any large opening into the sea, and this reef is probably connected with others, so as altogether to rut in an extent of upwards of 1000 miles, and hav ing a mean breadth of from 20 to 50 miles. These reefs sometimes give rise to islands. The coral rises above the surface of the water, disintegrates, becomes mixed with seeds of different kinds, carried by birds, floated by the waves. or wafted by' the winds. These grow and decay, and thus afford a more or less deep covering of soil, on which the cocoa nut and other large trees take root and grow. Palmerston island, the Island
of Tanea, the island of Middleburg, the island of Ton gataboo, the island of Mangea, and others in the South Sea, have a base of coral.
The following details in regard to the formation of coral reefs and islands, as given by Dr. Forster and Captain Flinders, will increase the interest of the pre ceding account. Dr. Forster remarks, ,4 All the low isles seem to me to be a production of the sea, or rather its inhabitants, the polype-like animals forming the litho phytes. These animalcules raise their habitation gra dually from a small base, always spreading more and more, in proportion as the structure grows higher. The materials are a kind of lime mixed with some animal substance. I have seen these large structures in all stages, and of various extent. Near Turtle Island, we found, at a few miles distance, and to leeward of it, a considerable large circular reef, over which the sea broke every where, and no part of it was above water; it included a large deep lagoon. To the east and north east of the Society Isles, are a great many isles, which, in some parts, are above water ; in others, the elevated parts are connected by reefs, some of which are dry at low water, and others are constantly under water. The elevated parts consist of a soil formed by a sand of shells and coral rocks, mixed with a light black mould, pro duced from putrified vegetables, and the dung of sea fowls ; and are commonly covered by cocoa-nut trees and other shrubs, and a few anti-scorbutic plants. The lower parts have only a few shrubs, and the above plants; others, still lower, are washed by the sea at high water. All these isles are connected, and include a lagoon in the middle, which is full of the finest fish ; and sometimes there is an opening, admitting a boat or canoe in the reef, but I never saw or heard of an open ing that would admit a ship.
The reef, or the first origin of these isles, is formed by the animalcules inhabiting the lithophytes. They raise their habitation within a little of the surface of the sea, which gradually throws shells, weeds, sand, small bits of corals, and other things, on the tops of these coral rocks, and at last fairly raises them above water ; where the above things continue to be accumulated by the sea, till by a bird, or by the sea, a few seeds of plants, that commonly grow on the sea shore, are thrown up and begin to vegetate; and by their annual decay and reproduction from seeds, create a little mould, yearly accumulated by the mixture with sand, increas ing the dry spot on every side; till another sea happens to carry a cocoa-nut hither, which preserves its vegeta tive power a long time in the sea, and therefore will soon begin to grow on this soil, especially as it thrives equally in all kinds of soil ; and thus may all these low isles have become covered with the finest cocoa-nut trees.
" The animalcules forming these reefs, want to shel ter their habitation from the impetuosity of the winds, and the power and rage of the ocean ; but as, within the tropics, the winds blow commonly from one quar ter, they, by instinct, endeavour to stretch only a ledge, within which is a lagoon, which is certainly entirely screened against the power of both ; this therefore might account for the method employed by the animal cules in building only narrow ledges of coral rocks, to secure in their middle a calm and sheltered place ; and this seems to me to be the most probable cause of THE