MODIFIED yy COMPRESSION. 149 
capable of forming a limeftone in a proper heat : That under 
86 atmofpheres, anfwering nearly to 3000 feet, or about half 
a mile, a complete marble may be formed: and laftly, That 
with a preflure of 173 atmofpheres, or 5700 feet, that is, little 
more than one mile of fea, the carbonate of lime is made 
to undergo complete fufion, and to act powerfully on other 
earths. rete 
Vill. 
Formation of Coal.— Accidental occurrence which led me to undertake thefe 
Experiments.—Refults extracted from a former publication. —Explana- 
tion of fome difficulties that have been fuggefted.—The Fibres of Wood in. 
Some cafes obliterated, and in fome preferved under comprefion.—Re- 
Semblance which thefe Refults bear to a feries of Natural Subftances de- 
Jeribed by Mr Harcuerr.—Thefe refults feem to throw light om the 
biftory of Surturbrand. 
As I intend, on: fome future occafion, to refume my ex- 
periments with inflammable fubftances, which I look upon as. 
far from complete, I fhall add but a few obfervations to what 
I have already laid before this Society, in the fketch I had the 
honour to read. inthis place on the 30th of Auguft laft. 
Tue following incidental occurrence led me to enter upon 
this fubject rather prematurely, fince I had determined firft to 
fatisfy myfelf with regard to the carbonate of lime. 
(OBSERVING, in many of the laft-mentioned clafs of “experi- 
ments, that the elaftic matters made their efcape between the 
muzzle of the barrel and the cylinder of lead, I was in the ha- 
bit, as mentioned above, of placing a piece of leather between. 
the lead and the barrel; in which pofition, the heat to which 
the leather was expofed, was neceflarily below that of melting 
lead. 
