Analytical Abstracts of Current 

 Literature. 



Conditions of Appalachian Faulting. By Bailey Willis and C. Wil- 

 lard Hayes. (Amer. Jour, of Sci. Vol. XLVL, pp. 257-269). 



The cross section of a great mass of sediments accumulated over a zone 

 parallel to the shore is that of a bi-convex lense. One edge rests against the 

 shore from which the mass at first thickens rapidly and then thins gradually 

 seaward. A broad shallow trough is thus formed by the deeper strata which 

 may be called an original syncline. The authors give data to show that pre- 

 vious to compression such original synclines of deposition existed in the 

 paleozoic strata of the Appalachians in Pennsylvania, east Tennessee, north- 

 west Georgia, Alabama and in other localities. 



In the original synclines of the Appalachian province the steeper seaward 

 dip was northwestward and the gentler shoreward dip was southeastward. 

 If strata in such a position be subjected to sufficient compressive force, the 

 original syncline will be exaggerated and the steeper shorter arm will be 

 rotated as between the forces of a couple. If compression is continuous 

 long enough the beds may be overturned. 



From this stepfold a thrust-fault may develop in either of three ways. The 

 pressure tending to exaggerate the fold is most efficiently transmitted by 

 the most massive stratum, and any condition which weakens this stratum may 

 lead to a fault. The three conditions under which this massive stratum 

 may be weakened are erosion, fracture, plastic flow ; the second being the 

 most common in the Appalachian region, where the massive stratum seems 

 to have fractured, forming thrusting faults under loads of 2,800 to 11,000 

 pounds per square inch, but to have folded without breaking under loads of 

 11,000 to 34,000 pounds per square inch. 



The authors discuss with the aid of diagrams the mechanics of repeated 

 parallel folds, and show that the parallel folds are later than that located by 

 the original syncline, and are consequent each upon the next preceding it in 

 time and position. In the Appalachians the compressing force was directed 

 both northwestward and southeastward. But when folding began there was a 

 movement from the force towards the resistance. This the authors conceive 

 to have been a superficial flow of a broad zone from northwest to southeast, 

 from the sea towards the land. H. B. K. 



