560 
P:aOFESSOIl JAMESON'S NOTES 
earth, that it is found in alluvial beds of clay, not as a 
secondary deposite, but as an original one; in short, 
that the diamond continues to form, or to use a more 
common language, to grow in alluvial districts in India. 
This opinion is not improbable, and nothing more seems 
to be necessary for the formation of the diamond in such 
situations, than time, or other favourable circumstances, 
for allowing portions of the carbonaceous matter in the soil 
to be reduced to the adamantine state, and afterwards to 
coalesce, according to the laws of affinity, into the granular 
and crystallised form, — in short, to form diamond. The 
gradual formation of calcareous grains, crystals and masses 
of calcareous spar in clays, of siliceous compounds in simi- 
lar rocks, appears to be occasioned by the gradual concen- 
tration of the calcareous and siliceous particles by some at- 
tractive power, in the same manner as we conceive diamonds 
may have been formed by the concentration of particles of 
carbon. 
The preceding details, in regard to opal and horn- 
stone, naturally lead us to inquire, if it is probable 
that the diamond, like these substances, is occasionally 
formed by the powers of vegetation ? Reasoning d priori, 
we would say it is much more likely that some plants would 
produce diamonds, than that they would secrete siliceous 
matter in a state fit to form opal and hornstone, because 
diamond is but carbon, the principal constituent part of 
plants, in a peculiar state ; whereas the silica of the opal 
and hornstone are subordinate ingredients in vegetation. 
But a direct appeal to the characters of some woods seem 
to countenance the idea I some years ago suggested in the 
Society, that vegetables may contain carbonaceous matter 
approaching to the adamantine state. Certain woods which 
have not the gritty feel of those that contain silica, are un- 
commonly hard, dark-coloured, and take a high polish; 
