OBSERVATIONS ON BASALT, &C. \\$ 



XIII. 



Ohjfe'rvalions on Bafalt, and on the Transition from the vitreous 

 to the Jl>tiy Texture, which occurs in the gradual Refrigeration 

 of melted Bafult; ivith fome geological Remarks. In a Letter 



from Gregory Watt, Efq. to the Right Hon. Charles 

 Greville, V. P. R. S. From the Philofophical Tranfaclions 



for 1804, p. 279. 



SIR, Soho, April 1804. 



-"- HE important geological confequences that feem de- Sir James HaTs 

 ducible from the changes of texture developed by Sir James ^ffl™"^™ 

 Hall's very judicious experiments on the regulated cooling oflation of fufed 

 melted bafult, induced me to attempt a repetition of them, bafalt * 

 fome time after the publication of his interefting and ingenious 

 paper. * I believe that formerly I had the honour of (bowing 

 you fome of the refults of my imperfedl and diminutive ex- 

 periments, which only ferved to afford additional proofs of the 

 tranfition from the vitreous to the llony texture, which takes 

 place in the gradual refrigeration of glafs. Circumftances 

 have prevented my refuming thele inveftigations, till it lately 

 occurred to me that fomething might be learned, by expofing 

 to the action of heat, a much larger mafs of bafaltic matter 

 than, as far as I am informed, had ever at one time been fub- 

 jected to experiment. 



One of the common reverberatory furnaces ufed in iron The experiment 

 founderies for the fufion of pig-iron, was ltTongly heated by a re P eated . on 7 



■ • , r r iu al lC T j j ., cwt- of rowley 



fire maintained for leveral hours. About leven hundred weight rag. 



of amorphous bafalt, here called Rowley Rag, was broken into 



fmall pieces, and depofited gradually on the elevated part of 



the interior of the furnace, between the fire and the chimney, 



from whence, as it melted, it flowed into the deeper part, in 



which, in ordinary operations, the melted iron is collected. 



It was obferved by the perfons attending, that it did not re-It was eafily 



quire half the quantity of fuel to fufe the bafalt, that would fu , fsd > f^form- 



^ * , . . , r . . ed perfect glafs > 



have been neceffary to melt an equal weight of pig-iron. w hen quickly 

 When the whole was melted, it formed a liquid glafs, rather coole(1, 



• Published in the TranfacYions of the Royal Society of Edin- 

 burgh, Vol. V. and in our Journal, Vol. V. quarto feries. 



Vol. X. — February, 1805. I tenacious, 



