AMBOIXA. 385 



island, a belt of living corals composed of a considerable 

 variety of species is easily accessible at low tide. Of these 

 corals the largest bulk is composed of massive Astrceids, of 

 which about ten different forms were collected. A massive 

 Forties is also very abundant. 



One species of "Brain Coral," and an Astrcea, form hu^e 

 masses, often as much as five feet in diameter, which have 

 their bases attached to the bare basaltic rock of the shore. 

 The tops of all of these coral masses are dead and flat and some- 

 what decayed : but on these dead tops fresh growth is now taking 

 place, showing that slight oscillations in the level of the shore of 

 a foot at least have taken place recently. The tops of the corals 

 have been certainly killed by being left exposed above water. 



Such slight oscillations are to be expected at the base of an 

 active volcano. The present re-growth is due to the corals 

 being now again submerged. The fact that these corals are 

 to be seen growing on the bare rock itself, and not on cUbris 

 of older corals, shows that the coral growth is very recent. 



The Brain Coral grows in convex, mostly hemispherical, 

 masses ; the Astrcea more in the form of vertically standing 

 cylindrical masses, or masses which may be described as made 

 up of a number of cylinders fused together. The masses of the 

 Astrcea are usually higher than those of the Mceandrina by about 

 a foot, because they are able to grow in shallower water, and 

 they thus range also higher up on the beach. 



Many of the masses of this Astrcea in the shallower water 

 are left dry at each low-tide, and appear to suffer no more in 

 consequence than do the common Sea-anemones of our English 

 coasts, which are so closely allied to them. T have not seen 

 any other species of coral thus growing where it is exposed at 

 low tide. The " Brain Coral " apparently cannot survive ex- 

 posure, and hence the tops of its masses have been killed during 

 the change of depth of the water at about a foot below the height 

 at which those of the Astrcea have perished. 



The common Mushroom Coral, so often to be seen as a chim- 

 ney ornament in England (Fungia sp.), is most extraordinarily 

 abundant on the shore, at a depth of one or two feet at low 

 water, and with it an allied larger, similarly free-growing coral 



c c 



