THE COASTS OF SICILY. 177 



were blooming in tufts of living flowers, or ramified 

 into little shrubs, every spur and bud of which was 



a most incredible rapidity. One generation builds its superstructure 

 on the stony beds formed by preceding polypes, until the entire 

 mass, increasing both in extent and thickness, finally reaches the 

 surface of the ocean. In the tropics most of these islands are sur- 

 rounded by a sort of rampart or breakwater, whose external walls, 

 which are almost always perpendicular, inevitably break in pieces 

 every vessel that strikes upon them. It is by a similar process that 

 the different seas of these regions are studded with rocks nearly 

 reaching to the surface of the water, and which are the more 

 dangerous to the navigator, in consequence of their escaping his 

 observation, while the depth of the sea surrounding them lulls him 

 into a state of deceptive security even in cases where constant 

 soundings are made. 



Coral islands consist of a narrow margin of slightly elevated 

 land, which in some cases circumscribes a very extended space. 

 This ring is either entirely formed by the coral structure, or by the 

 association of it with other rocks. The lake or lagoon which is 

 enclosed by this ring is sometimes very deep in all parts, at other 

 times it declines into a funnel-like excavation, while in some cases 

 it is interspersed with submerged rocks. There are, in general* 

 several narrow passages which communicate between the ocean 

 and the lagoon. In some cases, however, the ring is incomplete, 

 and is only represented by a large number of individual segments, 

 while, on the other hand, it is not unfrequently complete in every 

 part, forming a garland of verdure round a calm and motionless 

 lake, whilst the sea beyond breaks with violence against its coral 

 walls. The greater portion of these strange formations is neces- 

 sarily composed of the inner lake ; thus, for instance, the island of 

 Taritari presents a surface of 110 square miles, of which only four 

 belong to the land, the remaining 106 being composed of the 

 lagoon. 



Several theories have been advanced to explain the formation of 

 coral islands, and one of the most generally received opinions 

 consists in admitting the existence of numerous submarine craters, 

 the margins of which are at a depth suitable to the life and labours 

 of the polypes ; whilst the centre of the crater, and the sides of the 

 mountain from which it originates, have been suddenly engulfed in 

 VOL. I. N 



