Surface Geology of Burlington. 1051 
and the larger ones soon passing into small, broad, shallow drain- 
age basins, which impart to the central portion of the plateau a 
characteristic, gently undulatory appearance. To the northeastward 
is a small subsidiary plain of subdued undulatory topography, evi- 
dently in no way dependent upon the underlying stratigraphic 
rocks. It rises thirty or more feet above the broad alluvial flood 
plain of the Mississippi river, and is divided by the Flint creek. 
Southwestward it passes rather abruptly into the comparatively 
gentle slopes of the general plateau. It manifestly occupies the 
preglacially corroded valley of Flint creek, and laterally rests upon 
the irregularly eroded slopes of the ancient water course. A section 
of this limited auxilliary plain exhibits the following structure: the 
€xposure is continuous for nearly half a mile on Flint creek, and is 
practically similar throughout. 
SECTION I.' 
1. Course, brown, friable loam, with occasional small pebbles, 
gradating imperceptibly into No. 2......::cccccssseeeseeeee stress 3 feet. 
2. Yellowish-brown clay of a characteristic fisted nature ; con- 
taining a few small boulders or large pebbles, in places indietisoly 
laminated... isa 15 feet, 
3. Commingled “i wå ‘gravel irepabely sitsiilia: pebbles 
up to six inches in diameter, mostly rounded, erratic, but with 
numerous local angular flint and limestone pieces 10 feet, 
4. Drab, homogeneous unctuous clay. -2 feet. 
5. Coarse yellow and white sand, with a few small, erratic peb- 
bles, everywhere quaquaversally stratified... ERSE BO 
6. Very fine homogeneous white sand (this i is noe crete along 
Mee eitire sedioni. e a ac E 1 foot. 
7. Coarse yellow and white sand, with rounded and, nee 
erratic pebbles up to two feet in diameter, and larger local - ‘angular 
ss ee of flint and fossiliferous (Burlington) limestone, ex- 
a 
One mile above on Flint creek the coarse yellow sands form a 
conspicuous feature. A short distance further north the lower till, 
* The several sections selected are regarded as the most typical of the 
See exposures examined, and are marked on the accompany- 
ng ma map. 
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