VOL. XLVII.] PHILOSOPHICAL TRANSACTIONS. 165 



broad. The foot, trunk, and branches of this sea-production, are of one uni- 

 form matter : being formed of a substance homogeneous in all its parts, and of 

 a bark or coat. The substance forms the inner part of the coral ; and this, even 

 at the bottom of the sea, is nearly as hard as marble. At the ends of the branches 

 it is not so hard as the bark ; in some places near the ends it is of equal hard- 

 ness with it; but in the thick branches and trunk it is harder. 



This substance, being observed by a microscope, in corals of one colour, as 

 the red, and those which are not corroded by worms, appears uniform, smooth, 

 without spots of other colours, without holes or pits, being quite even, hard, 

 and capable of a perfect polish. But it is otherwise, in corals of more colours 

 than one ; as sometimes in those of a yellowish rose-colour, and those of a rose- 

 colour. For in some of these, the transverse sections exhibit different lines, or 

 annular bands (fig. 2, s, s, s, s,) of which one part is a rose-colour, and the other 

 yellowish, others white, and others more or less charged with colour, which 

 form concentric circles, a, like the coats of an onion. The same sort of annu-. 

 lar lines is observable in red coral a little burnt ; but they are of a grey colour, 

 and parted asunder by a line of a deep brown grey, (s, s, s.) 



When this substance, though very hard, happens to be stripped of its bark, 

 either by age, or accident, it is liable to a sort of teredo, or worm ; a small ani- 

 mal, that enters into the body of the coral by very small holes, (fig. 3, a, a,) 

 gnaws its inside, and makes itself roundish cells, (s, s.) These cells have a com- 

 munication with each other, (a, a,) and are separated by very thin partitions, 

 which weakens the coral extremely, and makes it brittle and improper for 

 any work. There is also another worm, which passes through the coral trans- 

 versely from side to side, and in right lines, by straight cylindrical holes. Even 

 the hardest marbles, lying in the sea, are liable to be corroded in the same man- 

 ner. The surface of the substance of coral is furrowed and wrinkled (fig. 4 and 

 2, e, u.) The wrinkles begin from the foot, and ascend, always nearly parallel, 

 to the trunk and branches. However, these wrinkles are not so deep in the 

 slender branches, and sometimes are not visible there : but they are always more 

 elevated, and more considerable, in the thick branches and trunk : they are not 

 smooth, but uneven, with knobs or bumps on them, and the surface composed 

 of very small hemispheres. 



This substance of the coral, being exposed to a strong fire, is reduced to a 

 very fine ash-coloured powder. As common ashes, when taken clean from 

 burning charcoal, and examined by a microscope, exhibit a sort of skeleton, 

 composed of the fibres and vessels of the wood ; so the ashes (of the substance) 

 of coral sufficiently show of what sort of parts it is composed. The microscope 

 discovers in it ashes formed of very small white corpuscles, united in clusters ; 

 each one of which is nearly spherical. The ashes of the bark of the coral are of 



x2 



