50 University Geological Survey of Kansas. 
the main features connected with it, but possibly differ in 
some minor points. 
The present physiographic features are dependent on two 
general conditions: First, a lithologic or stratigraphic, and 
second, orographic or earth movements. In the extreme 
northeastern part of the area in Missouri crystalline rocks of 
Archean age are found. There is substantial evidence that 
this section was brought into a dry-land condition in Pre- 
Cambrian time, and that it suffered a long period of erosion 
which resulted in cutting it into hills and valleys.  Be- 
ginning with Cambrian time a subsiding occurred which 
admitted ocean water to an unknown depth and the accumu- 
lation of stratified rocks of unknown thickness, and which 
probably represented a thickness sufficient, or almost suf- 
ficient, to cover the highest Archean hilltops now exposed. 
Subsequent to this a second period of elevation restored the 
area to dry-land condition and to erosive influence. When 
this second elevation was effected is somewhat uncertain, 
but as there is an absence of all rocks older than the Silurian 
throughout a wide area in this part of the state, it seems. 
probable that the elevation began not later than Carbonif- 
erous time. 
At present the Coal Measure rocks are scarcely known 
throughout the area of the Ozark dome, just here and there 
vestiges in the form of small areas protected from erosion by 
faults having occurred in such a way that portions of the 
rocks dropped down below their normal level. These vestiges. 
show that the Coal Measure rocks extended eastward at least 
as far as Aurora, and, therefore, to a certain extent, indicate 
something about the vast amount of erosion which has oc- 
curred since Coal Measure time. [From the general geologic 
conditions throughout the Coal Measures of northern Mis- 
souri, Kansas, and the Indian Territory, it seems probable 
that there was an elevation previous to Coal Measure time 
sufficient to produce the coastal or near-shore type of sand-. 
stone and shale nearly 100 miles or more to the west of the 
Missouri-Kansas line. There is a large area covered with 
hundreds of feet of Coal Measure formations, the sandstone and 
shale material of which probably came from the east or south. 
