24 Rk. T. CHAMBERLIN AND W. Z. MILLER 
1. Rotational Strains Developed by Bedding 
In the explanation worked out by Hayes for the Rome and 
Cartersville overthrusts of the southern Appalachians, the most 
important condition necessary for the development of such broad 
thrusts is stated to be the proper relation of rigidity of strata to 
superincumbent load.t An idea of the relative rigidity of the 
different strata in this portion of the Appalachians may be obtained 
from an inspection of the stratigraphic column. At the base of the 
exposed section are the Coosa shales which have a great, but 
unknown, total thickness and a minimum rigidity. Above these 
are several formations (Weisner quartzite, Rome sandstone, and 
Connasauga shale) of intermediate rigidity. These are then 
followed above by the Knox dolomite, a formation of unusual 
rigidity which consists of 3,500 to 4,500 feet of massive, cherty, 
dolomitic limestone almost wholly without bedding planes. Imme- 
diately upon this rest 1,200 to 1,800 feet of rigid Chickamauga 
limestone whose lower portion is nearly as massive as the Knox. 
There are, in these two formations, approximately 5,000 feet of 
strata with indistinct bedding and entirely without beds of shale. 
This gives them great competency when subjected to deformative 
stress. Above the Chickamauga limestone are several thin forma- 
tions of lesser strength, followed by 2,500 feet of very weak Floyd 
shale. This very weak series is followed in turn by several forma- 
tions of greater rigidity, namely the Oxmoor sandstone, Bangor 
limestone, and Coal Measure sandstone. This section may be 
generalized as follows: 
D—Moderately strong sandstones and limestones. 
C—Weak shales. 
B—Very rigid, massive dolomites of greath strength. 
A—At base very weak shales. 
It is the great competency of the thick dolomites, operating 
in conjunction with the incompetent beds above and below, which 
has controlled the deformation according to Hayes.? Quoting from 
Hayes’s explanation of his diagram (see Fig. 2): 
As already stated, the rigid mass B presents its weakest points where the 
compressing force exerts a shear across the beds—i.e., on the sides of the folds 
™C, W. Hayes, op. cit., pp. 150-52. 2 [bid., pp. 142-44. 
