Amongst the natural curiosities of Mauritius may be reckoned the Mare aux Vacouas, situate about two miles S. by E. of the Refuge.  It is an irregular piece of fresh water of about one mile in length, surrounded with many hundred acres of swampy land, through which run four or five little streams from the back hills; in some places it is from 20 to 25 fathoms deep, as reported, and is well stocked with eels, prawns and a small red fish called dame-cere, originally brought from China.  The eels and prawns are indigenous, and reach to a large size; the latter are sometimes found of six inches long without the beard, and the eels commonly offered for sale ran from six to twenty, and some were said to attain the enormous weight of eighty pounds.  This fish is delicate eating, and the largest are accounted the best; its form has more affinity to the conger than to our fresh-water eel, and much resembles, if it be not exactly the same species caught in the small streams of Norfolk Island in the Pacific Ocean.  Whence it is that fresh-water fish should be found on small islands, frequently at several hundred leagues from other land, will probably long remain one of the secrets of nature; if it were granted that they might come by sea, the difficulty would scarcely be less to know how they should have mounted precipices of many hundred feet, to reach lakes at the tops of mountains where they are not uncommonly seen.

Five or six miles to the south of the Refuge lies another lake of fresh water, called the Grand Bassin; its situation is more elevated than Vacouas, and except the ridges and tops of mountains, it seemed to be in the highest part of the island.  This basin is nearly half a mile in diameter, of a form not far from circular, and is certainly deep; but that it should be 84 fathoms as was said, is scarcely credible.  The banks are rocky, and appear like a mound thrown up to keep the water from overflowing; and the surrounding land, particularly to the south, being lower than the surface of the water, gives the Grand Bassin an appearance of a cauldron three-quarters full.  No perceptible stream runs into it, but several go out, draining through hollow parts of the rocky bank, and forming the commencement of so many rivers; the Rivieres des Anguilles, Dragon, and du Poste fall into the sea on the south or south-east parts of the island; the R. des Aigrettes before mentioned, and the R. Noire which runs westward, rise not far off, but their asserted subterraneous communication with the basin is doubtful.  No great difference takes place in the level of the water except after heavy rains; when the supply, which must principally come from springs in the bottom, so far exceeds the quantity thrown out, as to raise it sometimes as much as six feet.

On the western bank is a peaked hill, from which the Grand Bassin is not only seen to much advantage, but the view extends over great part of Mauritius, and in several places to the horizon of the sea.  It was apparent from hence, that between the mountains behind Port Louis and those of La Savanne to the south, and from the R. Noire eastward to Port Bourbon, not one-half, probably not a third part of the primitive woods were cut down; and this space comprehends three-fifths of the island, but excludes great part of the shores, near which the plantations are most numerous.