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visible a manner, that I thought I had sometimes ob- 
served her in the act. I have picked up shells at the 
moment when they were going to conglutinate them- 
selves with the stony matter that surrounded them; I 
have collected others half petrified. But what is more 
particularly interesting, is a bank of calcareous stone, 
which actually forms itself on the eastern part of the 
island of Omelmelek. It is there that I was enabled to 
remark all the stages of petrifaction, from the sand, or 
pulverulent detritus of the shells, to the rock already 
rendered solid; and what I found still more admirable 
on this scale of petrifaction was, that the powder of the 
shells already amalgamated, and become concrete, 
though still friable, and easy to be broken, is impreg- 
nated with a sort of volatile oil, which greased the fin- 
gers when touched with it. But this oil volatilized and 
disappeared in a short time. In the space even of a few 
feet, may be found all the gradations of petrifactions; 
that is to say, sand which does not cohere, sand in an 
incipient state of conglutination, sand resembling a sort 
of soft paste, paste beginning to harden, friable stone, 
soft stone, and hard stone. This gradation is even per- 
ceptible on the sea shore. I collected specimens of all 
these curiosities; but how much did it cost me to tear 
myself away from this interesting spot, without being 
able to make a multitude of observations, which might 
have contributed to the advancement of science. I re- 
commend the study of this bank to travellers who may 
visit this country. 
This species of stone is very white, and forms strata 
like slates. The houses and walls of Djedda and Jenboa 
are constructed of it. It is found in abundance upon all 
the coast, but principally in the labyrinth of isles and 
shoals called the isles of Ham a ra ? and form the most 
