Types of the Tertiary Peneplain. $5 
of the Carboniferous limestone and the Tertiary baselevel, this 
peneplain was formed up to the base of the steep plateau escarp- 
ment and far within the narrow limestone coves which indent 
its border. In the time that has elapsed since the formation of 
this pleneplain the streams have not been able to cut their gorges 
back to the escarpment, so their head-waters are still flowing 
upon that old plain, though at an altitude of from 1,000 to 1,100 
feet. Thus in a belt of country bordering the plateau on the 
west and extending northeastward from Huntsville, Alabama, 
to the Kentucky-Tennessee line the conditions were favorable 
for the production and have since been favorable for the perserva- 
tion of this peneplain. 
Across Kentucky the conditions were similar to those of Ten- 
nessee, except that the hard Coal Measure sandstones were less 
elevated and férmed no plateau, and subsequent erosion, as 
the Ohio river is approached, has been more and more active, 
until in the immediate vicinity of the river the pleneplain is 
recognized with difficulty. The conditions north of the Ohio 
river are at present entirely unknown, and the only suggestion 
the present writers can offer is that probably the two peneplains 
gradually approach each other in that direction until they 
practically coincide. 
About the southern margin of the province the elevation be- 
tween the two periods of baseleveling was so slight that the rocks 
have been practically exposed to: baselevel conditions from 
nearly the beginning of Cretaceous to Neocene time, and as a 
result are deeply decayed and but poorly preserve the records of 
the past. In the Coosa valley the Tertiary peneplain is gener- 
ally distinguishable, although subsequent erosion has cut deeply 
into its surface and, owing to the decay of the rocks, has reduced 
the least resistant members to a still lower baselevel—that at 
which the present streams of the region are flowing. Continuing 
eastward, the vertical interval between the Cretaceous and Ter- 
-tiary baselevels decreases and in the vicinity of Atlanta they 
practically coincide, so that the recognition of the two peneplains 
is almost impossible. The streams have not cut below the old 
peneplains in their upper courses and the tributaries of the 
Chattahoochee and Tallapoosa rivers still flow upon the surface 
of the Cretaceous peneplain. 
On the southeastern margin of the province, throughout the 
