Tetref action found at Eaft Lothian. 45 
of the weather, which we find in many inftances make 
a moft rapid progrefs. 
He alfo mentioned to me a very curious circumftance 
of his having found on the fea-coaft near Scarborough, 
many years ago, part of an horfe-fhoe incrufted with fea 
fand, which was fo concreted as to have acquired the 
hardnefs of common grit ftone, and retained the colour 
of the fand, with very little tincture of the iron ochre: 
and by the part which was left free from the incruftation. 
it appeared moft probable, that the horfe-fhoe had not 
been buried there many years, but had very recently ac- 
quired this incruftation upon that part only that was 
moft expofed to the wafhing of the fea water. 
Now, all thefe fa<Sts put together fcarce leave any 
doubt but that iron, and folutions of iron, do grealy pro- 
mote and haften the progrefs of all kinds of petrifaction ; 
and therefore, to purfue Lord bacon’s rule of induc- 
tion, deducing truth from a variety of faCts and experi- 
ments, all manifeftly and uniformly leading us to the 
fame conclufion, we may fairly infer, that whereas iron 
is of fuch manifeft ufe in the progrefs of vegetation, that 
plants are indebted for their green colour^, and for. 
(g) There are feme exceeding curious experiments and obfervations of Mr a 
delaval’s, tending to illuftrate this in the Phil, Tranf. vol. LV, 
Pr 3 6 . 37 - 
T 
many. 
