FOLDS AND MINOR THRUST-FAULTS. 473 



to unravel the complicated structure of the Coosa valley rocks have 

 proved unavailing, but more satisfactory results have been obtained in 

 the region south of the Coosa fault. 



Folds. — Probably in this region, as elsewhere in the Appalachians, the 

 first structural forms developed by horizontal compression were the ordi- 

 nary step-folds. These were doubtless modified by irregularities in the 

 original synclines of deposition, which are indicated by the unconformi- 

 ties and great variations in formation thicknesses. In the less compli- 

 cated portions of the region these folds remain more or less perfectly pre- 

 served, but generally they have been entirely obliterated by subsequent 

 faulting. 



Immediately south of Rome several short folds bring the Connasauga 

 shale above baselevel, and consequentl}^ give rise to narrow valleys, pene- 

 trating southward a few miles within the dolomite area. Each of these 

 folds, however, has been faulted along its western side. A similar faulted 

 anticline extends southward from Cave Spring. The extensive area of 

 dolomite, whose border is penetrated by these narrow anticlines, is a 

 broad, gently undulating sjaicline pitching southward. Its axis at 

 Cedartown is occupied by the overlying Chickamauga limestone and 

 Rockmart slate. An explanation of this broad area of practically undis- 

 turbed rocks adjacent to the intensely faulted region on the west will be 

 suggested below. 



In the region west of Cave Spring the folds which probably once existed 

 have been entirely obliterated, excepting a few very irregular synclines 

 in the faulted blocks of dolomite and possibly an anticline in the Rome 

 sandstone west of Exie. So far as tlieir structure can be determined, the 

 Frog Mountain sandstones form closed synclines, but these are secondary 

 structures, developed after the subterranes had already been folded and 

 eroded. 



Minor Thrust-faults. — The second type of structure is the normal AjDpa- 

 lachian thrust-fault, modified by the peculiar conditions prevailing in 

 this region. A great majority of these faults extend nearly due north 

 and south, and hence intersect the main structure axes of the region at 

 angles of 30° or 40°. Immediately south of Rome at least seven of 

 these minor thrusts occur within a belt three miles wide. They vary 

 in length from 3 to 8 miles and overlap along the strike. The strata 

 are thus cut into a number of narrow strips which form monoclinals 

 dipping steeply toward the east. In the vicinity of Cave Spring is 

 another series of faults similar in most respects to those south of Rome. 



Between Indian and Weisner mountains there is less regularity in the 

 arrangement of the minor thrusts, and their general trend is somewhat 

 east of north. A strip of Knox dolomite from one to four miles in width 



LXVl— Bull. Geol. Soc Am., Vol. 5, 1893. 



