336 REPORTS OX THE STATE OF SCIENCE. 



Coclivy. 



We reached Coetivy ou September 10, and remained for tifteen days, 

 while the ' Sealark went to the Seychelles for coal. The island was higher 

 than any we had up to that time visited, having wind-blown sand ridges 

 and hills up to 80 feet above the sea-level, arising on a flat coral reef. 

 Although situated only about 130 miles to the south of the Seychelles 

 Islands, the land fauna and flora are almost the same as on the islands of 

 the Chagos Archipelago, being scarcely richer. The plants, of course, in 

 the main necessarily govern the fauna, and it would appear to us that they 

 are in their turn governed rather by the nature of the soil — coral and coral 

 sand — than by their proximity to continental land. On the other hand, the 

 reefs of Coetivy showed in every group of marine animals a more varied 

 fauna than those of the Chagos, while very nearly all the species of the 

 latter seemed to be present. The I'eef on the eastern or seaward face of 

 the island was of a rather different character from any we had as yet seen, 

 being covered with Zoatera. There was also on the same part a consider- 

 able variety of nlgfo, but the edge and outer slope were, as elsewhere, 

 covered by corals and Nullipores. 



Farquhar and Providence. 



Leaving Coetivy we proceeded to a point about midway between 

 Madagascar and Farquhar Atoll, both to ascertain the depth and the 

 compass variation. The latter was almost the .same as at Mauritius, 

 situated 9 degrees to the south, while the depth, 1,856 fathoms, precludes 

 the idea of any close connection between the two localities. Farquhar, 

 which we then visited, was (as, indeed, were all the reefs we subse- 

 quently saw) remarkable for its reefs being almost completely covered liy 

 Zostera, both rim and lagoon. Its land attains a height of 75 feet, and is 

 clearly of the same formation as that of Coetivy ; it shows no trace of 

 elevation, and it has not been formed, as has been stated, by submarine 

 deposits. 



From Farquhar we proceeded to sound between the chain of islands 

 that extends between Madagascar and the Seychelles, and which would 

 appear to indicate a line of former connection. Between Farquhar and 

 Providence, 3:2 miles, we found 890 fathoms, and between the latter and 

 Alphonse-Francois, 155 miles, 2, 170 fathoms; while there were already 

 soundings of 952 fathoms between Alphonse and the Amirante group, 

 46 miles, and of 1,150 fathoms between the latter and the Seychelles, 

 32 miles. As the depth on either side is only about 2,300 fathoms, any 

 connecting ridge is comparatively low and of doubtful importance. 



From one dredging at 844 fathoms, 3 miles off the west of Providence 

 Reef, we obtained about 5 cwt. of stones, the largest about 2 feet in 

 diameter, together with some mud. The latter consists practically of 

 volcanic ash, while the stones are of three kinds — (1) manganese nodules, 

 formed round nuclei of ash ; (2) consolidated ash ; and (3) masses of 

 coral rock coated with manganese. It is clear that the existence of these 

 bottom deposits in such a position will have to be carefully considered 

 in connection both with the formation of Providence Reef and with 

 the existence of any former land between the Seychelles plateau and 

 Madagascar. 



Pierre Island^ 1 7 miles to the west of Providence Reef, and with a 



