484 
PALAEONTOLOGY OF ILLINOIS. 
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 separ¬ 
ated 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 notunfrequently 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 obtained 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 metamorphosed into sandstone, their mould preserves remark¬ 
ably well the scars of the point of attachment of the leaves, the wrinkles of 
the bark, etc., and show the gradual variations which modify the form of the 
cicatrices in passing from the stem to the roots. True petrified forests have 
been observed in banks of sandstone of the Coal Measures of Pennsylvania and 
of Kentucky. This phenomenon 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 in¬ 
closed 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 measures as in that so abundantly found in more 
recent formations; for example, in the Cretaceous and Tertiary beds of our con¬ 
tinent. The fracture of the pieces is of two kinds : either irregular, in vari¬ 
ous directions, like the breaking of mineral substances produced by hard strokes, 
or horizontal, as if by a kind of cleavage, the separate pieces forming disks or 
regular cylinders of various length. Generally, in both cases the fractured sur¬ 
face is clean, smooth, distinctly angular, and showing that in most cases, at 
least, the breaking of the trunks has been effected after the fossilization. Prof. 
Goppert, who has visited the fossilized forests of Egypt, south of Cairo, and 
has published the result of his researches*, has found there the trunks subjec¬ 
ted to a kind of multiple fracture, produced at various times and in various 
ways ; some of the trunks having their fractured surfaces obliterated as if by 
decay, others showing on their fragments, still closely approached to each oth¬ 
er, evidence of recent separation. He therefore explains their fracture as due 
to mere atmospheric influences, especially to sudden changes of temperature, 
which are not rare in those regions. This explanation could be admitted for 
*Der Versteinerte Wald by Cairo, &c.; Acad, der Weiss: zu Wien. vol. 38, 1858. 
