Vol. 51.] PHYSICAL FEATURES AND GEOLOGY OF MAURITIUS. 463 



30. The Physical Features and Geology of Mauritius. By Major 

 H. de Haga Haig, R.E., F.G.S. (Read April 3rd, 1895.) 



[Abridged.] 



[Plate XV.- Map.] 



I. Physical Features. 



The Island of Mauritius is the centre of a line of three — Reunion,, 

 Mauritius, and Rodriguez — some hundreds of miles apart ; they are 

 all volcanic, and in reality quite unconnected, except in so far as 

 they are on a line of volcanic action. Mauritius is about 40 miles 

 long and 27 miles broad, and it consists essentially of a mass of 

 volcanic debris thrown up from craters now extinct. A central 

 ridge, which is the main watershed of the island, and in which 

 are situated all the more recent craters, commences at the south, 

 where it has an elevation of about 2000 feet, and runs north- 

 wards, gradually curving to north-east. Tbe gentle slopes on each 

 side are stopped, round the greater part of the circumference, by 

 ranges of mountains up to nearly 3000 feet in height, so thin 

 and steep as to resemble walls. From the outer precipices of these, 

 comparatively level plains of variable width stretch to the sea. 

 There are three wide gaps in these mountains, through which the 

 slopes from the main watershed fall gently to the sea. The 

 northern part of the island — the pointed end of the pear — is cut off 

 from the rest by these mountain-walls, but the general direction of 

 the watershed continues across it at a much lower level, and is 

 even prolonged under water by a bank extending 14 or 15 miles 

 before it sinks to 100 fathoms below the sea : the general depth of 

 the sea-bottom around being about 1800 fathoms. The five or six 

 small islands to the north are on this bank, which also rises in 

 some places in the objectionable form of dangerous reefs, on which a 

 furious surf is always breaking. There is also a bank, 1 extending from 

 the south-western point of Mauritius (10 miles) towards Bourbon, 

 which appears to be a continuation of the central ridge. In fact, 

 Mauritius is on a line of weakness of the earth's surface, along 

 which volcanic disturbances have taken place. This line passes 

 through the volcanic islands of Rodriguez, Bourbon, and Madagascar. 

 From soundings taken round Mauritius and Bourbon, in connexion 

 with a scheme for laying a submarine telegraph-cable, it was found 

 that between the two there was a level sandy plain at a depth of 

 1800 fathoms, which extended all round Mauritius, except to the 

 north, where, as one of the men employed on the work stated, ' It- 

 was like sounding over precipices ; depths of 600 and 1300 fathoms 

 would often occur in close consecutive soundings.' It has often 

 been supposed that the Mascarene Islands were at one time united,, 



1 Called ' l'llot aux Pintades.' 

 Q. J. G. S. No. 203. 2 k 



