348 FOSSIL PLANTS. 
measures as in that so abundantly found in more recent formas 
tions; for example, in the Cretaceous and Tertiary beds of our 
continent. The fracture of the pieces is of two kinds: either ir- : 
regular, in various directions, like the breaking of mineral sub- 4 
stances produced by hard strokes, or horizontal, as if by a kind of, J 
cleavage, the separate pieces forming disks or regular cylinders 
of various lengths. Generally, in both cases the fractured surface a 
is clean, smooth, distinctly angular, and showing that in most 
forests of Egypt, south of Cairo, and has published the result of 2 
his researches,* has found there the trunks subjected to a kind of a 
multiple fracture, produced at various times and in various ways; 4 
some of the trunks having their fractured surfaces obliterated as 
if by decay, others showing on their fragments, still closely ap- 
proached to each other, evidence of recent separation. He there- 
fore 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 the . 
regular fragments of silicified wood, found in connection with our 
recent formations, and which, in some countries —in Arkansas- 
and Mississippi, for example—are in some places strewn upon 
the ground in profusion. Agglomerations of silex are rarely 
homogeneous or regularly compact throughout. They are inter- 
spersed with fissures or soft veins which, when penetrated by 
water, expand under the influence of frost, and determine frac- 
tures in various directions. But fossil wood broken in that way 
rarely found in our Carboniferous measures. Generally, the fossil 
trees of this formation, when separated from the mineral 
* Der Versteinerte Wald bel Cairo, &¢.; Acad. der Wiss. zu Wien, vol. 33, 1888 
