238 E. T. Long— Minor Faulting 



bank with a cliff facing N 48° E. This is most accessible 

 and where it crosses the bed of the creek gives a contact 

 reading for dip of nearly 2° N. This is undoubtedly too 

 high. Of all observed, here was found the best one for 

 measurements, along with several imperfect ones. Just 

 before the Encrinal layer crosses the creek a fault with a 

 dip of 25° N is exposed. Only the foot wall remains, thus 

 greatly facilitating the reading of both dip and striated 

 structure. The latter is N 4° E, the only positively 

 accurate reading for the direction of movement as shown 

 by the columnar structure on the fault planes. This read- 

 ing as all others is corrected for a magnetic declination of 

 8°, according to the U. S. G. S. quadrangle for the area. 

 The following table will give some idea of an average in 

 the faults : 



Faults dipping south Faults dipping north 



angle of dip direction of striae angle of dip direction of striae 



1. 20°-25° S. about N. 6° E. 20° N. about N. 6° E. 



2. 25° S. 28° N. N. 8° E. 



3. 30° S. N. 15° E. 22° N. N. 15° E. 

 strike about strike about 



N. 75° W. N. 75° W. 



4. 25° N. N. 4° E. 



strike N. 86° W. 



5. 30° N. N. 8° E. 



strike N. 72° W. 



Nos. 1, 2 and 3 occur just north of Crowbar where cliff and shore line = 

 N. 40° W. 



No. 3 is shown in fig. 5. 



No. 4 is in Salmon Cr. ; readings accurate within a fraction of a degree. 



No. 5 is at Portland Pt. 



For a discussion of the origin and results of rotational 

 strain, to which type of faulting the above appear to 

 belong, the reader is referred to C. K. Leith's "Struc- 

 tural Geology" and to the above mentioned article on 

 "Low- Angle Faulting." An attempted summary would 

 not do the subject justice, but two points may be empha- 

 sized. It is known that the great forces, which raised 

 thousands of feet of sedimentaries into the. Appalachian 

 Mts., were applied in a practically horizontal direction. 

 "The planes of greatest tangential stress should there- 

 fore dip at angles somewhere in the neighborhood of 45° 

 and may plunge downward or upward. ' ' 5 This angle of 



5 Chamberlin, E. T., Appalachian Folds of Central Pa., Jour. Geol., vol. 18, 

 p. 247, 1910. 



