I 88 STUDIES FOR STUDENTS 



hand it is certain that in many schists the actual shearing and 

 shortening is several times this amount. The major axes of the 

 flattened ellipses in the extreme phases of deformation are 

 sometimes from lo to 20 times as long as the minor axes. 



Relations of cleavage and fissility to faults. — It has been 

 explained that the shearing resulting in cleavage or the shear- 

 ing resulting in fissility may accomplish the same kind of defor- 

 mation as does thrust faulting.^ It is equally true that if, after 

 a fissility is produced, the rocks are under conditions of tension, 

 numerous minor slips along planes of fissility may result, the 

 effect of which is equivalent to normal faulting. In different 

 districts, in the Appalachians, for instance, at various places in 

 the Cranberry sheet, at Blowing Rock, N. C, and in Georgia and 

 Alabama, there have been observed during the past season the 

 results of widespread, somewhat uniformly-spaced, differential 

 movements between laminae at intervals varying from J^- to ^ 

 of an inch. In numerous cases, as a result of these differential 

 movements, the formations of district are brought into the same 

 abnormal positions as would be produced by ordinary normal or 

 thrust movement. The many slight differential movements 

 equivalent to thrust faults, so far as my obervations have gone, 

 are more frequent than the many slight differential movements 

 equivalent to normal faults. In the Cranberry area a granite- 

 gneiss, normally belonging below the Linville series, is brought 

 forward on the north and south sides of the area by innumer- 

 able minute movements between the laminae, to a position above 

 the Linville series. The same sort of irregular distribution due 

 to minute differential movements is seen in the formations of 

 the Linville series itself. In these cases one cannot find a certain 

 plane, or even a narrow zone, and say that here a fault has 

 occurred. However, it is certain that in a zone of considerable 

 width a differential movement has occurred as great as could be 

 accomplished by a great normal or great thrust fault. For this 

 particular form of deformation spread over a considerable area, 

 which does not have the clear cut character of an ordinar^y fault, 



^ Loc. cit., (A), pp. 659-660 ; (B), pp. 597-598. 



