Cretaceous Clays of Middle Georgia. — Ladd. 241 
The Cretaceous beds, at least those of the Potomac group, 
are visible at many points in cuts along the Central railroad, 
particularly between Columbus and Macon, and for many 
miles east of Macon both on the Central andthe Georgia rail- 
road. They consist mainly of white clays and sands, some- 
times wholly dififerentiated from each other. The cla\- is re- 
markably free from grit or sand, and the sand beds in turn 
are often entirely free from impurities of any kind. 
The Tertiary beds are exposed at many points along the 
dirt roads, chiefly east of Macon. Excellent sections of fossil- 
iferous marls of Eocene age are exposed in the railroad cut at 
Summit in the southern part of Jones county. 
The Lafayette and Columbia sands which over-spread the 
coastal plain may be seen the whole distance of the fall line, 
where thev have smoothed out the minor irregularities of the 
old land surface. They make a less fertile soil as a rule, than 
is found on the Piedmont side of the line. 
The Lafayette gravels are characterized b}' cross-bedding, 
rapid transition from coarse to fine materials, and, generally, 
by a deep red color resulting from the oxidation of iron bear- 
ing minerals. It frequently has a mottled appearance which is 
noticeable in the sides of gullies and cuts. The prevailing red 
color is frequently broken by a net work of grayish shades 
where the iron oxide has been "reduced" by organic com- 
pounds resulting from the decay of the roots of trees and 
shrubs. 
One of the most interesting sections along the fall line belt 
is at Rich hill, which has an elevation of seven hundred and 
fifty feet, is capped by Lafayette materials, and exposes in deep 
gullies on the southern side, one hundred and fifty feet of 
Tertiary strata, resting uncomformably upon the white Creta- 
ceous sands and clays of its base. 
Before the deposition of the great thickness of Tertiar\ 
upon the Cretaceous, much of the latter, especially along 
its land margin, was eroded, and re-deposited in the Tertiary 
seas. The subsequent removal of the Tertiary and overlying 
strata, has brought the Cretaceous rocks to the present surface 
over a considerable area in the western part of central southern 
Georgia. 
On the old geological maps of Georgia the Cretaceous de- 
