55$ 
PROFESSOR JAMESON'S NOTES 
% Hornstane, — We shall next trace the distribution 
and formation of hornstone. This mineral, which, in its 
pure state, is principally composed of silica, occurs in 
considerable abundance in several primitive rocks. It 
appears also in rocks of the transition-class, and is asso- 
ciated with different secondary rock formations. Wood, 
penetrated with hornstone, occurs occasionally in alluTiai 
strata, as in clays and sands of various kinds, and ex- 
hibiting such characters, as shew that the petrifaction or 
penetration of the wood with the hornstone, had taken 
place in it after it was enveloped in the clays and sands. 
Like opal, hornstone seems to be a product of vegetable 
origin; for the specimen which I now exhibit to the 
Society is a variety of woodstone. This remarkable spe- 
cimen, which is 18 inches long, 5 inches thick, and 8 inches 
broad, v/as torn from the interior of a log of teak wood 
{Tectona grandis)^ in one of the dock-yards at Calcutta. 
The carpenters, on sav/ing the log of teakwood, were ar- 
rested in their progress by a hard body, which they found 
to be interlaced with the fibres of the wood, and, on cut- 
ting round, extracted the specimen now on the table. This 
fact naturally led me to conjecture, that the mass of w^ood- 
stone bad been secreted by the tree, and that in this parti- 
cular case, a greater quantity of silica than usual had been 
deposited ; in short, that this portion of the trunk of the tree 
had become silicified, thus offering to our observation in 
vegetables, a case analogous to the ossifications that take 
place in the animal system. I was further led to suppose, 
that this wood might contain silica in considerable quantity, 
as one of its constituent parts, a conjecture which was con- 
firmed by some experiments made by Dr Wollastojj. 
Other woods appear also to contain silica, and these, in all 
probability, will occasionally have portions of their structure 
highly impregnated with silica, forming masses which will 
