FOSSIL PLANTS. 347 
times fruits of a hard consistence, rarely branches and leaves of 
ferns. They abound in the sandstone beds of our Coal Measures, 
and some of our new species of Lepidodendron and of Sigillaria 
have been described from specimens of this kind. In the second 
case of petrification, on the contrary, the surface or outside of the 
vegetables is generally obliterated, as if it had been more or less 
decayed while subjected to mineralization, while the internal struct- 
ure is preserved in its minutest details, and so distinctly, that it 
can be studied under the microscope when lamelle of the fossils 
are detached, and polished thin enough to become transparent. 
Specimens of wood fossilized in this way, though often remarked 
in the Carboniferous formations of Europe, and very common in 
the more recent formations of this continent, have rarely been 
found in our Coal Measures, and none as yet have been obtained, 
except from Southern Ohio and Northern Kentucky. Both these 
processes of fossilization have acted upon vegetables already sep- 
arated from their support, and more or less decayed, or upon trees 
still standing or still living, when they were surrounded by the 
mineral substances which caused their petrification. Though not 
quite as abundant as prostrated fossil trunks, petrified standing 
trees are not unfrequently obtained from the sandstone of our Coal 
Measures. Near New Harmony, Ind., some petrified trees, vary- 
ing in size from six to twelve inches in diameter, have been ob- 
tained from a sandy shale, and transferred to his museum in their 
standing position, and with their roots attached to the trunks, by 
my lamented friend, D. D. Owen. Though entirely metamor- 
phosed into sandstone, their mould preserves remarkably well the 
scars of the point of attachment of the leaves, the wrinkles of the 
bark, ete., and show the gradual variations which modify the form 
of the cicatrices in passing from the stem to the roots. True pet- 
rified forests have been observed in banks of sandstone of the 
Coal Measures of Pennsylvania and of Kentucky. This phenome- 
non should, therefore, demand but a passing notice, if it did not 
give rise to some discussions concerning the mode and cause of 
dislocation or fracture of these fossil trees, and also concerning 
the causes and agents of their petrification. 
Fossil trees, except when observed in their standing position, 
still half inclosed and sustained in the matter in which they have 
been originally buried, are always found in pieces or broken. 
This is observable as well in the fossil wood of the Carboniferous 
