E. Andrews on the Glacial Drift of Illinois. 77 
layers in - clay, the stratified character of the whole mass is 
clearly made out. 
e <a surprising phenomenon discovered, was the exist- 
ence all through the glacial drift, of numerous ee “ pockets” 
or cavities filled with stratified gravel. ‘These ets,” as 
the workmen called them, lay in all imaginable Me fa some- 
times with their strata set up at high angles. They were gene- 
rally from a few inches to a few feet in diameter, and terminated 
abruptly on all sides in the solid impermeable clay. The gravel 
as water-worn, and often so clean that it would scarcely soil a 
inci erchied Its interstices commonly contained a few gallons 
of water at the lower part, and some air or gas at the upper. 
The gas in many instances was inflammable, and was doubtless 
derived from the numerous boulders of highly bituminous lime- 
stone found in the clay. That the pockets were perfectly iso- 
lated is shown by the fact that though nearly eighty feet be- 
neath the surface of the lake, pat fee leaked a drop of 
water after they were once emptie e existence of these 
masses of gravel is very surprising. “The cavities, ipa emp- 
tied, looked exactly in many instances like the casts of rounded 
boulde I can only account for them by the licens that they 
were deposited as frozen masses of gravel, and thaw 
they were well deabodaied in the clay, leaving pee a in 
whatever position they happened to be put while 
After getting beneath the deposits made by the tie itself the 
excavations furnished not the slightest traces of any organic 
rema 
Sa the west shore of Lake Michigan, for a distance of over 
a hundred miles north of this place, the glacial drift rises som 
to notice any stratification, but to an observer stationed in a 
boat a hundred yards distant, dim but evident traces of a hori- 
ntal arrange a a appear. The strata = best seen by nanny, 
the level bands where the springs ooze o 
e more recent formation may aueae be noticed as a 
— stratified deposit filling the hollows or valleys of the older 
and rising to nearly the same height above the lake. It 
ilies belongs to the Champlain epoch. It is greatly to be de- 
sired that some geologist should thoroughly examine the recent 
geology around Lake Michigan, as there are problems of great 
Interest to be solved in connection with it; but as yet it is an 
anexplored field. 
, Nov, 26, 1866. 
