The Geologic llisfonj of Missoin-i. — l\'ii)sIoir. 89 
IVie Tertiary Epoch. — The conditions of Mesozoic stream 
trenching, land sculpturing and sub-aerial decay probabl}' 
continued well into the Tertiary epoch. Then, with the up- 
lift of the Avestern countr}^ a great change in the drainage 
took place ; divides were transferred westward to the Rock}^ 
mountains, and the Missouri river assumed something of its 
present proportions. It was probabl}^ somewhere about this 
time that the partial over-flow or great rise of the waters of 
southwestern Missouri took place, producing the deposits of 
gravel which are found along Spring river and other streams. 
All of the Ozark area proper, however, continued above water 
level and has, since that time, been subjected uninterruptedly 
to denudation. 
ConcUisions. — Among the more important facts brought out 
in this sketch are the long periods of sub-aerial decay to which 
the Ozark area has been subjected, especially the one since the 
post-Carboniferous uplift. The surprising thing is that the 
whole country has not been completely base leveled. Changes 
of level have doubtless prevented it in part; but. in addi- 
tion, the comparatively gentle slopes and the low altitudes 
and the absence of glacial action have supplemented this. 
The residuar}" products of decay have thus accumulated over 
the flat surfaces to great depths and they have protected the 
underlying rocks. The limestones, it is true, are not specially 
resistant, but the associated chert beds have shielded these. 
Further, from the fact that the climate was not arid and that 
the country is not and has not been at a great altitude, the sur- 
face has l)een well covered with vegetation. The declivities 
of the larger streams have not been great enough for them to 
corrade rapidly. To these causes we attribute the lasting 
qualities of this region. 
The earth movements which took place were ai)i)arent]3' of 
the njiture of great pulsations, alternately raising and lower- 
ing the surface. Along the eastern border, a shar[)er numo- 
cline was developed, as is exhibited in tlie comparatively steep 
dips of eastern Ste. Genevieve county. This feature accounts 
for the greater declivities of the streams toward the east and 
the proximity of the divides to the Mississippi river. The 
presence of the Archean rocks so near the surface liere, doubt- 
less had its influence in locatinu' this flexure. 
