15 



of the tubes, but in the substance of the coral, forming the sides 

 of the tubes. 



It appears, from the experiments of Mr. Hatchett, that the colour- 

 ing matter of the organ-pipe coral is similar to that of the red coral, 

 (gorgonia nobilis) being some unknown modification of animal matter. 

 The red colour of both these substances having been gradually de- 

 stroyed, during the action of the diluted nitric acid, as the solution 

 of the calcareous substance advanced ; and could not afterwards by 

 any means be restored : nor could any colouring principle whatever 

 be detected by the re-agents usually employed*. 



We also learn from the Count de Marsilli, that by digesting red 

 coral, with and without its membranaceous tunic, in milk, over a slow 

 fire, the colouring matter was dissolved by the milk, which became 

 thereby of a pink colour; whilst the coral became first of a saffron, 

 then of an ash colour, and at last of a livid white. The same effects 

 resulted from its digestion in heated wax. A similar deprivation of 

 colour is also found to take place in those pieces of coral, which, 

 having been broken, have fallen into, and have remained for some 

 time in the mud at the bottom of the sea-j~. 



As the colouring matter of these corals is capable of being thus 

 removed by digestion, it is not to be wondered at, that, in general, in 

 the fossil specimens, which must, in most instances, have been exposed 

 to long continued maceration in water, little or none of the original 

 colour remains. 



From the weight and other physical characters, as well as from 

 exposure to chemical agents, I found that every fossil of this species 

 in my collection, not imbedded in stone, contained too much siliceous 

 matter, to admit, by the agency of an acid, the examination into the 

 change which had taken place in the original constituent parts of the 

 coral. 



* Philosophical Transactions, for 1800. 



f Histoire Physique de Ja Mer, par Louis Ferdinand Corate de Marsilli. 



