188 PHOCEEDINGS OF THE GEOLOGICAL SOCIETY. [Feb. 20, 



stratum of sandstone than any of the others. This has been hol- 

 lowed by the waves in a remarkable manner, leaving channels and 

 ridges so sharp as to render walking over it a task of some difficulty. 

 In hollows sheltered by these ridges are some stumps of exogens, the 

 tops of which are quite level, and their substance much more solid 

 than that of those found elsewhere. Palms of large size appear to 

 have stood v^ery thickly here ; but not a single stump projects above 

 the surface, the force of the waves having washed them away, while 

 the more solid stems of the exogens resisted its action. This island 

 has no projecting border, nor have the others on the outer side. 



On the shore, immediately opposite two small islands of calcareous 

 rock, called Monkey Island and Rat Island, is a mass of the same 

 calcareous rock, about 400 yards in length, 50 in breadth, and 10 

 in height, lying on a bed of clay. Separated from this by a little 

 shallow bay about 50 yards wide, is another mass of the same rock, 

 about 100 yards long, and of the same width as the other. The 

 line of separation between the limestone and the clay is clearly de- 

 fined. It appears that formerly (but not at all within the remem- 

 brance of the oldest inhabitant) the projection of the limestone over 

 the clay, seaward, was much greater than at present ; and many 

 large masses, having lost their support, have fallen oif, and are lying 

 on the shore beneath, exhibiting a perfect correspondence in surface 

 at the point of fracture. The whole of this mass is free from the 

 sandstone covering, and exhibits no clear traces of having borne trees. 

 Its substance is permeated in every direction by crystals of carbo- 

 nate of lime, which, on the sea side, are covered with a pink in- 

 crustation consisting of oxide of iron. At the base of the superin- 

 cumbent mass is a bed of crystals of carbonate of lime, six or eight 

 inches in thickness ; and stalactites of curious forms depend from its 

 overhanging parts on the land side, where this mass abuts on a small 

 plain of ferruginous clay, in which are elliptical boulders of basalt, 

 which serve as nuclei to concentric layers of sand, hardened into 

 stone by a large portion of oxide of iron. This spot is overflowed at 

 high water ; and these nuclei project above the surrounding surface, 

 showing a clear section of their several enclosures. 



On various parts of the coast of Mauritius, masses of calcareous 

 stone, such as are here mentioned, are seen lying on the sand, but 

 always, I believe, in close proximity to the sea. Two such masses 

 exist at " Anse Bambou," in Grand Port, and one at Turtle Bay, 

 on the north-western side of the island ; and an islet at the en- 

 trance of the Grand Port, called " I'lle des Roches," is of the same 

 formation. This last is exposed to the action of powerful currents 

 on both sides, and has been considerably diminished in size within 

 fifty years. 



Great masses of coral, some of forty or fifty tons' weight, are seen 

 on various spots on the shores of Grand Port, at a distance of a 

 quarter of a mile from the sea, and at least fifty feet above its level. 

 These are of a species not now found here in a living state. 



Near the Chamarel Palls, at Blackriver, at about 900 feet above • 

 the sea, is a large quantity of old coral, of species still existing here : 



