Problems, Middle Mississippi River Region, Pleistocene Time 181 
Wittenberg in Perry County, Missouri, on the Missouri side of 
the river, and in most of the streams on the Illinois side in the 
Same latitude (Fig. 5). The terraces are regularly about 50 
feet above the highest portion of the flood plain of the 
Mississippi. Wherever sections of these terraces can be studied, 
they are clearly stratified and are composed chiefly of a loess- 
like silt, to a less extent of fine sand and, rarely, of fine gravel. 
The nearly constant difference between the elevation of the 
top of the terraces and the highest portion of the flood plain 
of the Mississippi strongly suggests that the terraces are frag- 
ments of a deposit made by the Mississippi when it was at a 
Stage at least 70 feet higher than the present mean datum plane. 
The composition of the terrace supports the idea that the sedi- 
ment came principally from the Mississippi, and not from the 
tributaries. The gradual slope of the tops of the terraces in the 
side valleys away from the master stream supports this idea. 
This gradual slope away from the master stream has been ob- 
served on several tributaries, and it is apparently a usual feature. 
Further evidence to be presented points to the same conclusion ; 
namely, that the sediment is derived principally from the master 
stream 
It is, therefore, believed that fragments of terraces, about 
70 feet above the mean datum plane of the Mississippi, or 50 
feet above the highest portion of the adjacent flood plain of the 
master stream, found in practically every tributary of the Mid- 
dle Mississippi River as far south as Wittenberg, Missouri, 
are fragments of a single deposit formed when the river was 
at a stage at least 70 feet higher than the present. Detailed 
work on these terraces shows that the gradient of the Mississippi 
at that time must have been about four inches per mile. The 
name Festus Terrace is proposed for the original fluvial plain, 
remnants of which may be found particularly well exposed near 
Festus, Missouri. 
A study of three tributaries of the Mississippi in Jefferson 
County, Missouri, and shown on the Kimmswick, Missouri- 
