286 Account of a Remarkable Fossil Tyce. 
limestone based upon floetz sandstone. This formation, 
which constitutes the north-eastern angle of the state of Illi- 
nois, where the waters of Michigan lake and the Illinois 
river often approach within a few miles of each other, and 
actually communicate at Chicago, continues east, and north- 
east, spreading in its course through Indiana into Ohio, and 
embracing the entire peninsula of Michigan. It is covered 
with a deposit of alluvial soil of a productive character, and 
presents to the eye a series of level prairies, interspersed. 
with occasional forests, and irrigated. by numerous small 
lakes and streams. ‘These features may be considered as 
peculiarly characteristic of the district of country drained by 
the rivers Kankakee and Des Plaines, which uniting their 
channels at the distance of forty miles south of Chicago, pro- 
duce the Illinois. ‘The junction is effected-on the southern 
slope of table and which confines lake Michigan to the 
north, at a point where the waters descend with considerable 
velocity, over a horizontal layer of shelving rock, which pro- 
duces a series of rapids, and is continually yielding to the 
action of the water; but there is nothing in the mineral 
physiognomy of the spot so remarkable as the petrified tree, 
which is found in the bed of the river Des Plaines about 
forty rods above its junction with the Kankakee. 
‘** This extraordinary species of phytolites occurs imbed- 
ded in a horizontal position in a stratum of newer floetz sand 
stone, of a grey colour, and close grain. There is now fif- 
ty-one feet, six inches of the trunk visible... It is exghteen 
inches in diameter at the smallest end, which appears to 
have been violently broken.off, prior to the era of its mine- 
ralization. The root-end is still overlayed by the rock and 
earth in the western bank of the river, and is two feet six 
inches in diameter at the point of disappearance ; but cir- 
cumstances will justify the conclusion that its diameter at the 
concealed end, cannot be less than three feet... The trunk is 
straight, simple, scabrous, without branches, and has the 
gradual longitudinal taper observed in the living specimen. 
It lies nearly at right angles to the course of the river, point- 
ing towards the south-east, and extends about half the width 
of the stream. Notwithstanding the continual abrasion to 
which it is exposed by the volume of passing water, it has 
suffered little apparent diminution, and is still firmly imbed- 
ded in the rock, with the exception of two or three places 
