Affinity between Bafaltes and Granite. 53 
The fame ftratum is perpetually varying in its mixture; and 
we (hould not too rigouroufly adhere to the proportion of in- 
gredients difcovered by the chemift in the hundred grains upon 
which his experiments may chance to be made. The fenfible 
qualities, the ftile of fiffure, the accompanying foffils, and the 
form of whole rocks, when furveyed by an experienced eye, 
are as good criterions of bafaltes as a certain proportion of iron, 
and the black glafs which it yields on fufion. Should the 
matter of any given rock contain too little iron to be fufible by 
the blow-pipe, and yet have other ftriking features of whin- 
ftone, would this be a fufficient reafon to conclude, that its 
formation has been different ? Chemiftry, if thus ftridly fol- 
lowed, would perplex mineralogy, inftead of reducing it to 
order. Charaders of minerals, purely chemical, would fepa- 
rate thofe whofe natural hiftory is alike, and bring together 
fuch as differ widely in their formation. 
The late Mr. Ferber’s letters from Italy furnifh fo many 
fads, confpiring in one way or another to (hew the affinity 
between bafaltes as well as other prcduds of fubterraneous 
fire and granite, that whoever reads them with this view will, 
I am perfuaded, find himfelf more interefted and inftruded. 
The following are among the moft ftriking of thefe fads. 
“ 4th fpecies of bafaltes. Oriental bafaltes through which 
“ the conftituent parts of granite are equably diffufed. Sepa- 
rate particles of red feldfpath, quartz, and mica, are 
“ difperfed through the fubftance of this fpecies : they feem to 
“ have been diftributed through an aqueous folution, and to 
“ prove, that this ipecies had rather an aqueous than a fiery 
“ origin.” I fee neither proof nor prefumption in favour of 
this fuppofition ; but in a feries of ipecimens, colleded with a 
view 
