XXIII. Experiments and observations on the Terra Ponderosa, &c

Abstract

This substance was got out of a lead-mine at Alston-Moor, in Cumberland. I first saw it in the valuable collection of my worthy and ingenious friend Matthew Boulton, Esq, at Soho; who, when he picked it up, conjectured from its weight that it contained something metallic. After two years ago I saw it in his possession; and partly from its appearance, being different from that of any calcareous spar I had seen, and partly form its great weight, I suspected it to be the spatum ponderosum.