918 Sand-Boulders in the Drift in Central Missouri. 
thirty-two feet (Professor Tracey). The country to the north is 
more or less underlaid by coal-basins. The undulations of this 
region were produced before the deposition of the Drift, as the 
denudation which removed the Coal-Measures excavated water 
courses out of the limestones. To these undulations the Drift 
conforms, and where cut through by the streams, these flow 
upon liméstone-beds, the higher layers of which abound in 
chert. E 
3. General Character of the Drift—At the University Gardens — 
the thickness of the Post-Pliocene deposits reaches twenty-nine — 
feet; at the University, more than twenty-two feet; but in the | 
bed of a stream immediately to the westward it thins out. e 
upper two to three feet consists of highly-calcareous, clayey soil . 
different from the poorly-calcareous Drift (A, Fig. 1). The Drik 
consists of a drab, hard, sandy clay, very much cracked and 
stained with iron, —bright yellow-red; or occasionally with mat- d 
ganese,—bluish-black (Fig. 1). The staining is superficial, and 
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the mottled appearance has been produced since the sine 
of the clay. The clay.is rudely stratified, as shown in à pt 
out, where a torrent has cut through it (fifteen to twenty she 
thick). The lower portion contains fragments of chert from 
subjacent rock, and occasional boulders of granite, ee 
and quartzite, which rarely occur higher in the clay- 
boulders seldom reach two feet in diameter, although, eighty 
ninety miles to the northward, there is an erratic oie 
hundred and twenty-five tons’ weight; but the margin 
Drift is not far distant to the southward. Enclosed i gi 
