I8.J6.] THEIR RELATION 1 TO VOLCANOES. 351 



Hence in these cases it would appear, that volcanos burst forth into 

 action and become extinguished on the same spots, accordingly as 

 eltvatory or subsiding movements prevail there. Numberless facts 

 could be adduced to prove that upraised organic remains are common 

 wherever there are active volcanos ; but until it could be shown that in 

 areas of subsidence, volcanos were either absent or inactive, the 

 inference, however probable in itself, that their distribution depended 

 on the rising or falling of the earth's surface, would have been hazardous. 

 But now, I think, we may freely admit this important deduction. 



Taking a final view of the map, and bearing in mind the statements 

 made with respect to the upraised organic remains, we must feel 

 astonished at the vastness of the areas, which have suffered changes in 

 level either downwards or upwards, within a period not geologically 

 remote. It would appear, also, that the elevatory and subsiding 

 movements follow nearly the same laws. Throughout the spaces 

 interspersed with atolls, where not a single peak of high land has been 

 left above the level of the sea, the sinking must have been immense in 

 amount. The sinking, moreover, whether continuous, or recurrent with 

 intervals sufficiently long for the corals again to bring up their living 

 edifices to the surface, must necessarily have been extremely slow. 

 This conclusion is probably the most important one, which can be 

 deduced from the study of coral formations; and it is one which it is 

 difficult to imagine, how otherwise couldi ever have been arrived at 

 Nor can I quite pass over the probability of the former existence of 

 large archipelagoes of lofty islands, where now only rings of coral-rock 

 scarcely break the open expanse of the sea, throwing some light on the 

 distribution of the inhabitants of the other high islands, now left standing 

 so immensely remote from each other in the midst of the great oceans. 

 The reef-constructing corals have indeed reared and preserved wonder- 

 ful memorials of the subterranean oscillations of level ; we see in each 

 barrier-reef a proof that the land has there subsided, and in each atoll 

 a monument over an island now lost. We may thus, like unto a 

 geologist who had lived his ten thousand years and kept a record of the 

 passing changes, gain some insight into the great system by which the 

 surface of this globe has been broken uo, and land and. water interchanged. 



CHAPTER XXL 



MAURITIUS TO ENGLAND. 



Mauritius, Beautiful Appearance of Great Crateriform Ring of Mountains- 

 Hindoos St. Helena History of the Changes in the Vegetation Cause 

 of the Extinction of Land-shells Ascension Variation in the Imported 

 Rats Volcanic Bombs Beds of Infusoria Bahia Brazil Splendour 

 of Tropical Scenery Pernambuco Singular Reef Slavery Return to 

 England Retrospect on our Voyage. 



April 2gth. IN the morning we passed round the northern end of 

 Mauritius, or the Isle of France. From this point of view the aspect 



