PREGLACIAL VALLEVS OF THE MISSISSIPPI. 763 
uplift, or whether it was subject to periods of deepening, between 
which were periods of equilibrium, when the force of the stream 
was expended in broadening the channel. 
An important feature connected with the development of the 
preglacial drainage of this region has received thus far but little 
attention, namely, variations in stage of development displayed by 
the drainage lines in different parts of the Mississippi basin. 
My attention was first called to the matter when studying 
southern Illinois, in the autumn of 1892. It was found that 
there is a great scarcity of deep buried valleys, compared with 
their number further north. It is only at rare intervals that a 
well on the uplands fails to strike rock within a few feet of the 
level of the upland plain. The main preglacial valleys of this 
region are cut to but moderate depths, seldom showing an exca- 
vation of more than 100 feet below border districts. Upon dis- 
cussing this matter with Professor Chamberlin it was found that 
he had noted a similar feature in the unglaciated part of Mis- 
souri, near Sedalia. The greater part of the surface is unfur- 
rowed by drainage lines. The few which occur have reached 
only an adolescent stage of development. The appearance is as 
if an uplifted base leveled region had been subjected to erosion 
for an insufficient time to allow well developed systems of 
drainage to be inaugurated. Further north (and especially in 
northern Illinois and the driftless area of Wisconsin) the pre- 
glacial systems had dissected the uplands quite thoroughly. 
though the altitude is not much greater than southern Illinois 
and scarcely so great as the region around Sedalia. Krom what 
is now known, it seems probable that the northern districts suf- 
fered uplift long before the southern. A thorough investigation 
of this matter will doubtless bring out a very interesting his- 
tory, showing an increasing extent and degree of uplift proceed- 
ing from certain centers of upheaval, by which the peneplain of 
the Cretaceous and early Tertiary periods rose and became trans- 
formed into the more or less deeply channeled uplands of the 
early Pleistocene. 
FRANK LEVERETT. 
Denmark, Iowa, May 23, 1895. 
