'•W)i Tlie ^liiieric((ii (ieijloijist. DcccmiuM-. isii.i- 
tlieiu, l)iit wherever the surface erosion and small j>'ullies are 
stiKlie<l it is j'ound to be similar in amount to tliat on both 
the (\)lunil»ia loams of the South, and the Mississippi and 
Missouri loess deposits of the North. Moreover, the subsi- 
dence of the Ozarks, which their phenomena clearly indicate, 
was undoul)tedly contemporaneous with tiiat of all the sur- 
rounding- regions, and they were merely a portion of the 
great tract which participated in the epeirogenic movement 
of d('pr<'ssion characterizing the Columbia epoch. The amount 
of this depression below the present level of the country was 
variable in the Ozarks. Although perhaps only a few hun- 
dred feet in the southern part, it was undoubtedly 400 to 600 
feet throughout the central portion, antl perhaps 1,000 feet 
or more at the northeastern corner of the uplift. 
In ai)proaching St. Louis from the west on the St. L. & 
S. F. railroad, the loess or (Jolumbia loam is tirst observed on 
the upland ridges in the vicinity of C'uba, at an elevation 
slightly exceeding 1,000 feet above the sea. Thence to the 
Mississippi river this loam is found to overspread the surface, 
excepting where, as on steep hillsides, it has been removed by 
erosion; and it increases in thickness as lower levels are 
reached, and especialh'^ along the streams, imtil it connects, 
after having passed over the Meramec highlands, with the 
undoubted Mississippi loess at St. Louis. This same bed of 
clay or loam rests on the eastern slope of the Ozark plateau 
south from this line, but terminates, as 1 am informed, at 
])rogressively lower levels until it connects with the undoubted 
jnarine Columbia deposits of the embaynient region. The 
great depression and partial submei-gence of the Ozark area 
here indicated is amply sufHcient to account for the per- 
manentl}^ flooded but sluggish condition of the streams in the 
valleys of the central and western portions of the ])lateau. 
POST-CIOLUMBIA ELEVATION. 
Since the Columbia epoch the valleys of the Ozark region 
have been gradually assuming their present aspect. First, 
there was an elevation to approximately the i)resent altitude. 
The region undoubtedly participated to a certain extent in 
the minor movements of neighboring regions later in the 
Glacial period: ])ut these movements were comparatively^ 
slight and had little eHect -(ui the erosive ])ower of the streams. 
