8 R. T. CHAMBERLIN AND W. Z. MILLER 
from the crest of a broad anticline by erosion. When subjected 
to further lateral thrust, the upper beds on one limb of this anti- 
cline, encountering little resistance in front, ride forward over the 
subaérial surface. Related to this form of erosion-thrust is another 
special type described by Hayes from the southern Appalachians. 
Thus the field of the low-angle fault is not an unexplored one, 
since explanations have been offered for certain special types of 
overthrusts. The very definite explanation for the Rome and 
Cartersville overthrusts of the Southern Appalachians was worked 
out by Hayes as early as 1891.2 The key of this explanation was 
suggested by the massive and peculiarly competent dolomite 
formations which alternate with weaker shale layers. In this 
= 3 Rigidity 
= eh 
=— : =—= 3 = ===) Medium 
===> Sea Ze ee ES Minimum 
E “eth Maximum 
—— ——— SZ <=. > 
Aa SSS +=<4 Minimum 
7 ———— 
if 
Fic. 2.—A theoretical section to represent the position of the fault plane (PP’) 
in the Rome and Cartersville thrusts. From Hayes. 
type of deformation the strata are thought to have first flexed into a : 
pair of gentle anticlinal bends some notable distance apart. 
Between the flexures the strata remained essentially undisturbed. 
Finally a break occurred near the crest of one of the anticlines, and 
the thick, competent formations sheared more or less horizontally 
along a slippage plane which followed closely the bedding of the 
weak shales (Fig. 2). 
The erosion-thrusts of Willis and the special form so clearly 
described by Hayes are dependent upon appropriate rock strata and 
structure, and thus these explanations, while they fit admirably the © 
conditions in the southern Appalachians for which they were 
devised, do not apply to various other overthrusts where the 
necessary stratigraphic conditions do not obtain. They thus con- 
stitute a particular type due to special conditions. They do not 
apply to the very remarkable overthrusts of the Scottish High- 
« Bailey Willis, ‘‘Mechanics of Appalachian Structure,’ U.S. Geol. Surv., 1 30h 
Ann. Rept., Part II (1893), pp. 222-23. 
2C. W. Hayes, loc. cit., II (1891), 141-54. 
