146 C. W. HAYES OVERTHRUST FAULTS OF THE APPALACHIANS. 



ous rocks are highly fossiliferous and there can be no mistaking their age. 

 They form an oval area about three-fourths of a mile wide and two miles 

 long. The strata are disposed in a gentle anticlinal, or rather a quaqua- 

 versal, elongated in a north and south direction, apparently a continuation 

 southward of the Chatoogata mountain axis. This area of Carboniferous 

 rocks is entirely surrounded by Cambrian, the younger strata dippiug under 

 the older with apparent conformity. West of this Carboniferous island there 

 is a broad expanse of highly contorted Coosa shale extending to Sugar val- 

 ley, where Carboniferous rocks are again found dipping eastward under the 

 Cambrian. The Carboniferous rocks come up in an anticlinal forming Sugar 

 valley ridge, on the west of which they again dip under an arm of Coosa 

 shales which terminates a short distance to the north, but is continuous 

 around the south end of the anticlinal with the great body of shales to 

 the east. 



On a section northwestward from Rome (the Rome section, figure 2, plate 

 3), a very similar succession is met with. A short distance west of the city 

 the Floyd shales are found dipping southeastward under the Coosa. Pass- 

 ing the Horseleg mountain anticlinal they dip to the northwest under a 

 narrow arm of Coosa, which occupies the synclinal between the Horseleg 

 mountain and Beech creek anticlinals. Beyond the latter they dip under a 

 second and broader arm of Coosa, which lies in the synclinal between the 

 Beech creek and Lavender mountain anticlinals. 



The present relation of these rocks is manifestly the result of a fault by 

 which the older rocks were thrust from the east over upon the younger 

 on a plane which coincides approximately with the bedding, and which has 

 been subsequently thrown into a series of gentle folds. The greater part of 

 the overthrust rocks have been removed by erosion, and both Cambrian and 

 Carboniferous shales are at the base-level of Coosa river. Their line of con- 

 tact is therefore the intersection of an undulating thrust plane with a hori- 

 zontal base-level plane. Wherever the folding subsequent to the thrust has 

 brought the thrust plane below the present base-level, there the overthrust 

 rocks have been preserved, while those resting at higher levels have been 

 entirely removed. The distance through which the older strata have been 

 moved westward upon the horizontal thrust plane is, in the Sugar valley 

 section, about four and one-half miles, and west of Rome at least four miles ; 

 and there is reason to suppose that in the latter section the thrust was two 

 or three miles greater. 



Coosaville-Mound Mountain Division. — Between Coosaville and Round 

 mountain the course of the fault is about east and west. The evidence of 

 considerable folding, faulting and erosion prior to the overthrust is more 

 marked in this division than at any other point. North of the east-and- 

 west fault line are two synclinals forming Gaylor's ridge (^K, map, plate 2)^ 



