ify aed eahinaiNe Diskt Xen sesleelis 
Exposure of Living Corals to Sun and Air.—(p. 94.) 
Mr. Berre JuxKes, in his account of the voyage of the “ Fly,” recently published, men- 
tions that he observed about the Australian reefs, living Astras, the tops of which at 
low tide were 18 inches above the water ; and he adds, that he believes an exposure to 
the sun and air for two or three hours will not kill many polyps. 
On Dolomisation.—(p. 153.) 
The experiments of von Morlot, alluded to on page 153, are properly a confirmation 
of a view previously presented by Haidinger. As early as 1827, this author, in an 
article on pseudomorphism, described certain dolomitic pseudomorphs, and stated that in 
their formation “ part of the carbonate of lime was replaced by carbonate of magnesia, so 
as to form in the new species a compound of one atom of each,” (Trans. Roy. Soc. 
Edinb., March 19, 1827.) Elie de Beaumont, in 1837, suggested the same view, and 
thus accounted for the occurrence of open spaces in the dolomite, often amounting to 
twelve per cent. of the mass. Haidinger, observing the frequent occurrence of gypsum 
and dolomite in the same beds, concluded that the sulphate of magnesia was the agent by 
which the change was produced, in the manner stated on page 154, and confirmed by 
von Morlot. Some heat is required, according to these authors, for this result, 
The theory of dolomisation, to be complete, must meet the cases presented by the 
coral rocks, in which the calcareous material is subjected to the ocean, whose waters 
contain for the most part a magnesian ch/orid instead of su/phate ; and farther, no heat 
can be supposed to have been concerned. ‘The limestones of the western of the United 
States, are nearly true dolomites in composition, since they contain, according to Mr. D, 
D. Owen, from thirty to forty-five per cent. of carbonate of magnesia. Yet they are 
compact rocks, that present no evidence of the action of heat during their formation or 
since. We may believe that the result is due to a simple reaction of the carbonate of 
lime and certain oceanic salts present ; but the process needs illustration by actual experi- 
ment. 
Chalk of Oahu.—(p. 150.) 
This chalk consists simply of the comminuted corals and shells of the reef. It has 
been examined microscopically by Prof. J. W. Bailey, at the request of the writer, and 
found to be destitute of the minute organisms abounding in the chalk of England, 
