C m 1 
XI. Observations on Basalt, and on the Transition from the 
vitrebus to the stony Texture, which occurs in the gradual Refri- 
geration of melted Basalt ; with some geological Remarks. In 
a Letter from Gregory Watt. Esq. to the Right Hon. Charles 
Greville, V. P. R. S. 
Read May 10, 1804. 
SIR, Soho, April io, 1804. 
*1 he important geological consequences that seem deducible 
from the changes of texture developed by Sir James Hall's 
very judicious Experiments on the regulated cooling of melted 
Basalt, induced me to attempt a repetition of them, some time 
after the publication of his interesting and ingenious Paper.* 
I believe that formerly I had the honour of showing you some 
of the results of my irnperfect and diminutive experiments, 
which only served to afford additional proofs of the transition 
from the vitreous to the stony texture, which takes place in the 
gradual refrigeration of glass. Circumstances have prevented 
my resuming these investigations, till it lately occurred to me 
that something might be learned, by exposing to the action of 
heat, a much larger mass of basaltic matter than, as far as I am 
informed, had ever at one time been subjected to experiment. 
One of the common reverberatory furnaces used in iron 
founderies for the fusion of pig iron, was strongly heated by a 
fire maintained for several hours. About seven hundred weight 
* Published in the Transactions of the Royal Society of Edinburgh, Vol. V. 
MDCCCIV. O O 
