425 
of Edinburgh , Session 1867-68. 
President, about twenty years later, on the death of Henry Duke 
of Buccleuch, in 1811. It was objected that many of the rocks, 
whose structure was ascribed to fusion by Hutton, become, on cool- 
ing from fusion, a slag or a glass, and cannot afterwards recover 
their crystalline texture. It was also objected that carbonate of 
lime, which constitutes a large proportion of the stratiform beds in 
the crust of the earth, cannot be fused, because, long before the 
heat is raised high enough, it parts with its carbonic acid and 
becomes lime, which proves refractory under the most intense 
artificial heat which can be applied. Hutton’s answer was that 
Nature’s operations in this matter are carried on upon a vast scale, 
with unlimited heat, and under enormous pressure — three condi- 
tions wholly unlike those in which all experimental imitations 
must be attempted. Hutton, in his Dissertation seems to have 
anticipated these objections. But though a skilful and inven- 
tive chemist, he did not venture to meet them by experimental 
evidence. He even threw discouragement over the proposals of 
his enthusiastic disciples to find a reply by daring to drag Nature 
into their laboratories. “What!” said he, in a different essay, 
“judge of the great operations of the mineral kingdom from 
having kindled a fire and looked into the bottom of a little 
crucible ! ” 
Sir James Hall, however, resolved not to be thus discouraged. 
Such was his veneration for his friend and teacher, that he tells us 
he would not execute his plan during the lifetime of Hutton. But 
after Hutton’s death Hall kindled his fire, and looked into his 
little crucible; when behold! Nature at work there, exactly as in 
the vast profound. 
In a paper on granite, read to the Society in 1790, he pointed 
out, that, although the quartz, felspar, and mica, which make up 
that rock, are fused into glass by artificial heat, there is no reason 
why, under slow cooling, the crystals of felspar, quartz, and mica 
should not separate and crystallise apart, in the same way as the 
crystalline particles of salt and ice separate in the freezing of sea- 
water, or like the crystallisation which renders transparent glass an 
opaque, rock-like body, when from a state of fusion it is made to 
consolidate very slowly by gradual cooling. 
Sir James tells us afterwards that, at the time this paper was 
