Account of a Remarkable Fossil Tree. 289 
species of petrification me be found. At a short distance 
above, where the bed of the Des Plaines approaches nearer 
the summit level, aiedede ensues, and continues from that 
point northward to the shores of lake Michigan. In the vi- 
cinity of Chicago, where this limestone is quarried for eco- 
nomical purposes, it is characterized by the fossil remains of 
molluscous, and other aquatic animals. 
“* There exists a water communication between the head 
of lake Michigan and Chicago, and the river Des Plaines, 
during the periodical rises of the latter, but its summer level 
4s about seven feet lower, at the termination of the Chicago 
portage, than the surface of the lake. From this point to its 
Junction with the Kankakee, a computed distance of fifty 
miles, she bed of the Des Plaines may be considered as hav- 
ing a mean southern d of ten inches per mile, so 
that the floetz rocks at its mouth, lying ona level of tony 
eight feet eight inches below the ‘surface of lake Michigan. 
have an altitude, which cannot vary far, from five hundred 
and fifty feet above the Atlantic. ‘There are no mountains 
for a vast distance either east or west, of this stream = it is @ 
country of plains, in which are occasionally to be seen allu- 
vial hills of moderate elevation ; but the most striking ine- 
qualities of surface proceed fr rom the streams which have 
worn their deep-seated channels through it; and an oceanic 
overflow, se of covering the country, and producing 
these strata by deposition, would also submerge all the im- 
mense tracts of secondary and alluvial country, between the — 
Alleghany and the Rocky Mountains, converting into an arm 
of the sea, the great valley of the Mississippi, from the 
Gulph of Mexico north, to the Canadian lakes. We find in 
the alluvial soil along the Illinois and Des Plaines, blocks of 
granite, hornblende, and gneiss, cor rm: the same appear- 
ances of attrition, and of having been transported from their 
parent beds, which characterize shi secondary table lands 
the margin of the great American eae the prairies o¢ 
Illinois, and the western parts of New-York 
“ The c along both banks of the river Des Plaines, 
at the spot where this imbeded fossil tree occurs, is a level 
and beautiful prairie, ‘covered with a luxuriant growth of 
grass, and interspersed with small groves of oaks and hicko- 
tert: quercus alba, and one squarrosa, of the Amer- 
ican 
