Eskers of the Kansan Epoch. — Ilershcii. 207 
entire course; (e) whether the ice was in motion during the 
existence of the streams ; and (d) whether the front of the 
ice-sheet remained stationary during the entire period in 
which these deposits w^ere formed. 
It is necessary, first, to determine the origin of the material ; 
and this may be divided into two classes, foreign drift and 
local material. To the former class are referred all pebbles 
and boulders which have come from a greater distance than 
the western edge of the Niagara terrane in southeastern Wis- 
consin and northeastern Illinois. In the latter class are in- 
cluded pebbles of Galena limestone, white chert from the 
residuary clay of the Galena terrane, and the Freeport gravel.* 
None of tlie so-called local material has come from a greater 
distance than sixtj^ miles. Consequently, when we find that 
at least 90 per cent, of all the material of a size exceeding one 
fourth of an inch, in the gravel-knolls and ridges, is of the lo- 
cal class, we know that at least that percentage of the coarser 
portion of the deposit was gathered up within sixty miles from 
its present position. But when the percentage of local and 
foreign drift is studied in detail in the several knolls, it be- 
comes yet more significant. Two miles east of the city of 
Freeport, several knolls, standing well out from the rock 
slopes of the valley, are found to consist to the extent of 95 
percent, of Freeport gravel and highly ferruginous sands, 
which were probablj' derived from the same formation. The 
courses of the streams that deposited these knolls can be 
traced eastward along various ridges and mounds for about 
three miles, and in every exposure of the interior nearly the 
same percentage of Freeport gravel prevails. So far as traced, 
tliese streaius nowhere come in contact with the rock ridges 
which bound the valley. Just south of and parallel with the 
*The Freeport pfravel is an ancient river-gravel, in which the pebbles 
are light brown in color and mostly have a peculiar semi -pDJished ap 
pearance. It has never been observed in situ within th<^ district, al 
though intelligent well-drillers report penetrating occasionally at a 
moderate depth in the larger valleys, a red gravel quite distinct from 
the drift, both lithologically and stratigraphieally. From that deposit 
the brown river gravel distributinl through the drift of the Pecatoniea 
valley has probably been derive.l. Further evidence of its local origin 
will be presented in the text. Its designation as Freeport gravel is in 
tended as temporary, until its true nature can be ascertained or it can 
be correlated with gravels discriminated and specifically designated in 
some other district. 
