Mauritius. paet i. 



shorter axis, measured across from the inner sides of 

 the mountains near Port Louis and those near Grand 

 Port, being no less than thirteen geographical miles in 

 length. M„ Bailly boldly supposes that this enormous 

 gulf, which has since been filled up to a great extent 

 by streams of modern lava, was formed by the sinking 

 in of the whole upper part of one great volcano. 



It is singular in how many respects those portions 

 of St. Jasfo and of Mauritius which I visited agree in 

 their geological history. At both islands, mountains 

 of similar external form, stratification, and (at least in 

 their upper beds) composition, follow in a curved chain 

 the coast-line. These mountains in each case appear 

 originally to have formed parts of one continuous mass. 

 The basaltic strata of which they are composed, from 

 their compact and crystalline structure, seem, when 

 contrasted with the neighbouring basaltic streams of 

 subaerial formation, to have flowed beneath the pressure 

 of the sea. and to have been subsequently elevated. 

 We may suppose that the wide breaches between the 

 mountains were in both cases worn bv the waves, 

 during their gradual elevation — of which process, within 

 recent times, there is abundant evidence on the coast- 

 land of both islands. At both, vast streams of more 

 recent basaltic lavas have flowed from the interior of 

 the island, round and between the ancient basaltic hills ; 

 at both, moreover, recent cones of eruption are scattered 

 around the circumference of the island ; but at neither 

 have eruptions taken place within the period of history. 

 As remarked in the last chapter, it is probable that 

 these ancient basaltic mountains, which resemble (at 

 least in many respects) the basal and disturbed remnants 

 of two gigantic volcanos, owe their present form, struc- 

 ture,, and position, to the action of similar causes. 



St. Paul's Rocks. — This small island is situated in 



