394 ON THE GROWTH OF 



it. For why should this Bald-Head differ from Mount 

 Gardner, which, although close by it, is formed of primi- 

 tive rocks ? Besides, Peron says, that it has the same geo- 

 logical constitution. (T. ii. p. 133.) 



At Rota, one of the Marian Isles, M. Gaudichaud, 

 detached from the limestone rock, at about a hundred 

 toises [above the level of the sea, branches of true, ma- 

 drepores, in perfect preservation. Here are, then, three lo* 

 calities in which they are found at great heights. We 

 have observed them, say the French naturalists, at infinite- 

 ly lower elevations in several other places, as at the Isle 

 of France, where they form a bed' more than six feet 

 thick, between two streams of lava ; at Wahou, one of the 

 Sandwich Islands, where they have not a greater elevation, 

 but extend for several hundred toises over the surface 

 of the island. In all these cases, it is necessary to distin- 

 guish between the lithophy tes, which have, by their living 

 powers, formed continuous masses, from those which, after 

 having been rolled about, broken down by the water, 

 and mixed with sea shells, contribute to form those depo- 

 sits known by the name of madrepore limestone. The 

 latter sort is nothing but the debris of the former. De- 

 posits of this description occur in the Marian Isles, and 

 in those of the Papous ; they occur also on the coasts of 

 France, and in several other places. 



It would appear from observations made in Timor and 

 other places, that the species of the genus Astraea which 



fers from the elevea others, is composed of a solid limestone rock, in 

 which veins of calcedony are observed. Does not this small island, we 

 may ask, indicate that some cause has prevented the madrepores from 

 covering it, while they constructed their habitations in the neighbour- 

 hood, on bases which probably must be of the same nature as those of 

 the small island ? 



