310 
EXPERIMENTS ON INCRUSTATIONS. 
I have assumed that the incrustations near Simon’s Town are of 
a similar nature to those found in New Holland, because the descrip- 
tions of authors correspond with the appearances I have witnessed, 
and because I have compared a specimen from New Holland with 
those I obtained at the Cape, and can trace no essential difference 
either in their external characters or chemical composition. Peron 
appears to have been the only one who has supposed any of the New 
Holland specimens of vegetable origin ; and even he considers the 
calcareous bodies discovered on Bald Head and on the island of Timor, 
in which they occur in large quantities at considerable elevations, 
as really corals, but has not stated any reasons for his opinion, 
beyond their general resemblance to those bodies. On Bald Head, 
however, Captain Flinders discovered “ two broken columns of stone, 
three or four feet high, formed like stumps of trees, and of a thickness 
superior to the body of a man appearances elsewhere found by 
Peron, and described by him as being of vegetable origin. 
In the hope of obtaining more precise information respecting the 
nature of the Cape specimens than could be derived from their 
external characters, I submitted them to the analysis used by Mr. 
Hatchett* to determine the composition of different madrepores, 
de ceux dont l’industrie humainc fait usage: de meme que, dans nos ateliers, c’est en 
melant avec le sable du rivage ces debris calcaires pulverises par faction des flots, qu’elle 
parvient a former un veritable ciment calcareo-quartzeux, d’une qualite superieure, il est 
vrai, mais tres-analogue d’ailleurs a ceux que l’art produit. Voyages aux Terres 
Australes. Tom. 1 1. p. 169 et 70. 
En brisant les rameaux de ces especes de lithophytes lorsque l’incrustation est recente, 
on apper^oit le tissu ligneux engage dans un etui solide, et sans aucune alteration remar- 
quable; mais a mesure que fenveloppe calcaire augmente, le bois se desorganise et se 
change insensiblement en un de detritus acide et noiratre: alors l’interieur du tube est 
encore vide, et conserve un diametre a-peu-pres egal a celui de labranche qui lui a servi 
de moule ; enfin le tube finit par s’obstruer et se remplir de parties quartzeuses et cal- 
caires : quelques annees s’ecoulent et tout est converti en une masse de gres. A cette 
derniere epoque, la forme arborescente seule peut rappeler f etat ancien de vegetation. 
Ibid. p. 171. 
* Philosophical Transactions for 1800. 
