334 REPORTS OX THE STATE OF SCIENCE. 



enormous numbers on certain isLands, though it was mid-winter ; crab- 

 plover, curlew, whiuibrel and a sandpiper were common, and in the 

 north-west monsoon buzzards, kites, pigeons and crows are said to be 

 regular visitants. The green and shell turtles {Chelone mydas and 

 C. imbr-icata) abound, the former coming on shore to deposit its eggs at 

 night, and the latter in the daytime. The only other reptiles are a marsh 

 tortoise, perhaps introduced from Madagascar, and geckoes ; there are no 

 amphibia. There is only one land shell, and arachnids and myriapods 

 are scanty ; the land Crustacea are similar to those of the Maldives, but 

 the coco crab (^Blrgus latro) is also abundant. Mr. Bainbrigge Fletcher 

 sorted the insects, and found about 110 species, most of which are pro- 

 bably indigenous, but the best season for the group would be in the 

 rather hotter and damper north-west monsoon. On the whole, the land 

 fauna and flora are much what one would expect to get, regarding the 

 Chagos as a group of purely oceanic islands. 



Mauritms. 



We arrived at Mauritius on August H, and remained two weeks, 

 "etting certain heavier dredges made, and examining its coasts. The reefs 

 vary from fringing to barrier, the best example of the latter being at 

 Grand Port, where it is four miles from the land. It has thei-e a few 

 small islets of somewhat metamorphosed coral rock, varying up to 

 40 feet high. At first it seemed as if they might have been formed by 

 hurricanes and blown sand, but we discovered the same rock in the im- 

 mediate vicinity, overlying a basalt, 70 feet above the water. The pre- 

 sent islets probably represent the remains of a considerable island, 

 elevated for at least 100 feet, extending along that part of the barrier 

 reef. 



Leaving Mauritius on August 21, we had three days' dredging and 

 sounding off its reefs. The contour is the same as that of atoll-reefs, a 

 »radual slope to 40 fathoms, succeeded by a steep to IHO fathoms, tlien 

 tailing off in five miles to 1,000 fathoms. The bottom at 1-50 fathoms 

 was covered with heavy blocks of coral from the reef above. At 300 

 fathoms we found shell and small pieces of coral, and further out a 

 bottom of bare coral mud, sweepings from the reef and land. 



Caryados Carajoa. 



Between Mauritius and Cargados there was a depth of 1,962 fathoms, 

 there being no marked connecting ridge, though the bottom tails off very 

 gradually from each bank.^ At Cargados we remained for six days, 

 examining the reefs and islets, and dredging. It is a crescent-shaped 

 surface I'eef, 31 miles long, on the south part of the Nazareth Bank, 

 which is, roughly, 220 miles long by 60 broad, with an average depth 

 of 33 fathoms. The land is of coral rock with no signs of elevation, and 

 is a great breeding-resort for sea birds. It is covered with guano, owing 

 to wliich the land flora is very scanty, only 18 different plants being 



o 



' The Hydrographer, Rear-Admiial Arthur M. Field, informs me that a bank with 

 a depth of about 30 fathoms has been discovered rather to the east of this soundiuo:. 

 It is hence probable that there is a shallow ridge connecting Mauritius and Cargados. 

 Its presence should be shown, too, in ihe bottopa samples between the two localities. 



