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1060 OW Upham— Minnesota Valley in the Ice Age. 
ified drift which is probably an interglacial formation, supplied 
* the time of final melting of the earlier ice-sheet and spread 
ond its receding margin upon the unchanneled surface of 
the till that had been formed during that earlier part of the ice 
e. The upper bed of till, thus apparently representing the 
stratified yellowish gravelly clay, containing occasional rock 
fragments up to six or eight inches in diameter, but showing 
only two or three of larger size, these being two to three feet 
in diameter. The bottom of this upper till, seen clearly ex- 
posed along a distance of about 250 feet, is an almost exactly 
level line. Next below is the modified drift which is supposed 
to have had its origin from the melting ice-sheet of the earlier 
Glacial epoch. Its thickness is also sixteen to eighteen feet and 
consists of yellowish gravel and sand, containing pebbles up to 
x or eight inches in diameter, quite ferruginous in the lowest 
one to three feet, levelly stratified throughout, but having the 
horizortal layers often obliquely laminated, the dip of this 
lamination being to the east or northeast, toward the Minnesota 
river, and varying in amount from two or three to fifteen or 
twenty degrees. The underlying till was seen along an extent 
of 100 feet, the greatest depth cut into it being about eight _ 
feet. Its upper line, separating it from the modified drift, is 
approximately level, but undulating, with its highest points 
two or three feet above the lowest. This till, like the upper 
ars no marks of stratification; and ne ither sbows any 
interbedding or transition, but both are bounded by definite 
lines, at their junction with the intervening gravel and sand. 
The lower bed of till is’ aR bluish, excepting for about twenty 
feet from the face of t uff inward, where weathering has 
changed it to the same sehen color that characterizes the mod- 
ified drift and upper till. In other portions of the Minnesota 
valley, its bluffs frequently exhibit modified drift interbedded, 
sometimes in deposits of large extent and thickness, with the 
till, oy makes up the principal mass of these bluffs and of 
the drift-sheet. 3 
peculiar stratification observed in several of the deposits 
of clay which form part of the terraces of modified drift in the 
Minnesota valley in Scott and Carver counties, belonging to 
the time of departure of the last ice-sheet, appears to afford a 
measure of the rate of deposition. In Mr. Charles Rodell’s 
excavation for brick-making at Jordan, the clay is bedded in 
distinct horizontal layers from three to eight inches thick, aver- 
aging six inches. These layers are dark bluish, often ‘finely 
laminated, changing above and below toa nearly black, more 
unctuous and finer clay, — — the partings between 
