74 EFFECTS of HEAT 
refting problems that has ever engaged the attention of men of 
{cience. 
He fuppofed, 
I. Tuar Heat has acted, at fome remote period, on all 
rocks. , 
II. Tuar during the action of heat, all thefe rocks (even 
fuch as now appear at the furface) lay covered by a fuperin- 
cumbent mafs, of great weight and ftrength. 
III. Tuar in confequence of the combined action of Heat 
and Preffure, effects were produced different from thofe of heat 
on common occafions; in particular, that the carbonate of 
lime was reduced to a ftate of fufion, more or lefs complete, 
without any calcination. 
Tue effential and characteriftic principle of his theory is thus 
comprifed in the word Compreffion; and by one bold hypothefis, 
founded on this principle, he undertook to meet all the objec- 
tions to the action of fire, and to account for thofe’ circum- 
ftances in which minerals are found to differ from the ufual 
products of our furnaces. 
Turs fyftem, however, involves fo many fuppofitions, appa- 
rently in contradiction to common experience, which meet us on 
the very threfhold, that moft men have hitherto been deterred 
from the inveftigation of its principles, and only a few indivi- 
duals have juftly appreciated its merits. It was long before 
I belonged to the latter clafs; for I muft own, that, on read- 
ing Dr Hurron’s firft geological publication, I was induced to 
reject his fyftem entirely, and fhould probably have continued 
ftill to do fo, with the great majority of the world, but for my 
habits of intimacy with the author ; the vivacity and perfpicui- 
ty of whofe converfation, formed a ftriking contraft to the ob- 
{curity 
