DEFORMATION ANTECEDENT TO OVERTHRUST. 147 



and Dirt Seller mountain {L). Their axes trend N. 45° E. and pitch to 

 the southwest. Both of these synclinals are terminated by transverse faults 

 across their southern ends. The formation of the synclinals and the faults 

 by which they are terminated evidently preceded the overthrust, since they 

 have only slightly affected the regularity of the thrust plane. Thus the 

 fault which shears off the eastern side of the Dirt Seller mountain synclinal 

 and at Gaylesville brings the Connasauga shales in contact with Carbonifer- 

 ous rocks passes under the thrust plane without apparent disturbance of the 

 latter. The Coosa shales rest upon all the formations from the upper Cam- 

 brian, Connasauga, up to the Floyd shales. A short distance west of Coosa- 

 ville a small area of Coosa shales rests upon the upper beds of the Knox 

 dolomite, being wholly detached from the main body of Coosa toward the 

 south. This is the only point in this division where the evidence of a broad 

 overthrust is apparent, and it is probable that the inclination of the fault 

 plane is somewhat greater than it is further northward. 



Round Mountain- Gadsden Division. — From Round mountain to Gadsden 

 the intersection of the thrust plane with the present land surface follows 

 approximately parallel to the eastern edge of Lookout mountain. This 

 parallelism would indicate a comparatively steep hade for the fault, but that 

 it is in reality even here a broad thrust is shown by the presence, five miles 

 east of Gadsden, of an isolated area of Knox dolomite which has been ex- 

 posed by the erosion of the overlying Coosa shales. This relation of the 

 dolomite to the overthrust shales is exactly the same as that between Car- 

 boniferous and Cambrian shales occurring west of Kesaca, as already de- 

 scribed. 



The continuation of the Rome fault southward beyond Gadsden has not 

 been studied in detail. It is apparently replaced by several faults with the 

 steep hade of the east Tennessee type, which shear off the eastern sides of 

 the Cahaba and Coosa coal fields as shown by Squire and McCalley.* 



Cartersville Thrust Fault. 



Position of the Fault. — The Cartersville fault passes entirely across the 

 area represented in the map (plate 2) in a direction strikingly parallel with 

 that of the Rome fault already described. Its northern extremity is prob- 

 ably a few miles beyond the edge of the map, thougli with regard to its exact 

 termination there is still some question. 



In consequence of the induration of the rocks east of the fault, its position 

 is clearly indicated by the topography. The metamorphic rocks form a 

 nearly continuous line of bluffs from one to three hundred feet higher than 

 adjacent portions of the valley. These bluffs are the western escarpment of 



*"Mapof the Cahaba Coal Field and Adjacent Regions;" Joseph Squire and Henry McCalley, 

 Report Geo!. Sur. Ala., 1890 (in press). 



