40 W. Upham—Minnesota Valley im the Ice Age. 
go through sand and gravel, sometimes with layers of clay, to 
the depth of 75 or 100 feet, finding till below. At Belle 
Plaine the sand and gravel are about fifty feet deep, underlain 
by till. Shakopee prairie has forty or fifty feet of this modi- 
fied drift, lying upon limestone. The principal remnant of 
these deposits seen below Shakopee was a terrace about seventy- 
five feet high, an eighth to a third of a mile wide and four 
miles long, extending through Eagan in Dakota county, its 
north end being about two miles south of Fort Snelling. i 
valley was first excavated in till which rises in continuous 
bluffs on each side 50 to 100 feet above these high plains and 
terraces of modified drift. It was afterward filled along this 
distance of one hundred miles next to its mouth with fluvial 
of Paleozoic tim 
Scanty exposures of Cretaceous strata are found in many 
parts of Minnesota, enclosing sometimes marine shells, some- 
times impressions of leaves, and at a few places thin layers of 
lignite. The western two-thirds of the State were probably cov- 
ered until the glacial period by deposits of this age which have 
now been mainly oreided, with much from the underlying Pale- 
ozoic rocks, and constitute a part of the drift, irrecognizably 
mingled with detritus and bowlders that have been brought 
from Laurentian and Huronian areas far to the north and north- 
east. Excepting its partial submergence by the sea in the Cre- 
rt 
sissippi River and valley has probably existed since the middle 
