EROSION ANTECEDENT TO OVERTHRUST. 149 



and conglomerates — the Ocoee group of Safford— shows a progressive re- 

 gional metamorphism. In the Hiwassee section most of the intervening 

 lithologic varieties are present between the unaltered shales and the crystal- 

 line schists, while on the Pinhook section these intervening rocks have been 

 removed. 



Inference as to Amount of horizontal Thrust. — If the progress of metamor- 

 phism toward the east was regular along this whole line from Hiwassee river 

 to Esom Hill, we may infer from the width of the strip of semi-metamorphic 

 rocks something as to the amount of thrust which has taken place. The 

 width of tliis belt on the Ocoee is about twelve miles, while at Pinhook creek 

 it is less than one mile. Hence the thrust at the latter point must be, on 

 the assumption of uniform metamorphism, not less than eleven miles. 



Phenomena at the Thrust Plane.— The inclination of the thrust plane is 

 frequently so low as 5° and is rarely more than 25°. In all of the many 

 sections examined, the rocks on opposite sides of the fault are apparently 

 conformable, and while in the few localities in which the exact contact was 

 observed the strata immediately at the fault show considerable distortion, 

 this extends only a few feet on either side ; so that in most sections there is 

 no indication of faulting except the abrupt transition from unchanged to 

 metamorphic rocks. 



Probable Age of the Ocoee Group. — As to the age of the Ocoee group there 

 has been little, if any, evidence discovered in the area represented in the 

 accompanying map. The rocks have as yet yielded no fossils, and they are 

 separated by a fault of unknown displacement from rocks whose age can 

 be determined by paleontologic evidence. The work of Willis and Keith 

 in east Tennessee, however, has firmly established the position of a corre- 

 sponding group in the Big Butt range and east of Chilhowee mountain as 

 belonging to the upper Silurian, and the rocks are continuous from one 

 region to the other. 



Hypothesis of Erosion prior to Thrust. — Assuming the age of the semi- 

 metamorphic series to be Silurian, it will be observed that the Carters ville 

 fault does not ordiaarily place older rocks upon younger, but leaves forma- 

 tions in their proper relative position while one or more intervening mem- 

 bers are wanting. Thus, at Holly creek, the Silurian Ocoee slates rest upon 

 Cambrian shales, and the intervening Knox dolomite is wanting. The re- 

 lation of the formations is represented in the generalized section (figure 4, 

 plate 3). The hypothesis which most readily explains this relation is that 

 of extensive erosion prior to the thrust. The probable condition preceding 

 the faulting may be represented by the ideal section 1 (figure 4, plate 3), in 

 which the plane of subsequent thrust is represented by the heavy broken 

 line T T. It will be observed in section 2 (figure 4, plate 3) that if the strata 

 were removed down to the line A B the same superposition of older strata 



XXII— Bull. Geol. Soc. Am., Vol. 2, 1890. 



