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XX. An Analyjis of Two Mineral Subjlances , viz. the Rowley- 
rag-ftone and the Toad-ftone. By William Withering, 
M. D. ; commuicated by Jofeph, Prieftley, LL. D. F. R. S .. 
to Sir Jofeph Banks, Bart. P. R. S. 
Read May 16, 1782. 
TO SIR JOSEPH BANKS, BART. F. R. S.. 
DEAR SIR, 
Birmingham, 
0£t. 1, 1781. 
1 HAVE the pleafure to lay before you an analyfis of two- 
mineral fubftances by Dr. withering of Birmingham, 
whole accuracy in proceffes of this kind will, I doubt not, 
give you and the members of the Royal Society great fatif*- 
faflion. 
It may, perhaps, throw fome additional light on the fubjeft 
©f thefe foffils to inform you, that the Rowley-rag appears-, 
by its texture before and after fufion, and alfo by the quantity 
and quality of the air which it yields in fulion, to be the fame 
thing with the bafaltes with which you have favoured me from. 
Scotland ; and that the Toad-ftone, treated in the fame man- 
ner, appears (after the calcareous part has been diffolved out of 
it) to referable lome of the lpecies of lava, except that it yields 
much more air. As Dr. withering has fent Ipecimens of the 
foffils in their natural fate, I thought it might not be amifs to 
prefent along with, them the glajjy fubfta?ices into -which they 
^re reduced by fulion. 
] am, with the greateft refpect, See. 
J, PRJESTLE Y, 
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