212 



W. M. DAVIS NOMENCLATURE OF SURFACE FORMS 



tude, and relative resistance ; and as to the fault, the stage of erosion 

 that has been reached with respect to it in whatever cycles of erosion that 

 have left visible traces; also whether the fault line is marked by scarps 

 or valleys, and if so of what kind, and so on. A more satisfying physio- 

 graphic description of the district here imagined might therefore be 

 phrased as follows : 



An important fault line, trending about northeast-southwest, sepa- 

 rates a northwestern body of massive crystalline rocks, evenly covered 

 by an alternating series of hard red sandstones and weak shales, dip- 

 ping southwestward about 30°, from a southeastern body of younger, 



Figure 5. — An imaginary Example nf a resequent Fault-line Scarp 



nearly horizontal, weak, gray sandstones and marls. The rolling uplands 

 of crystalline rocks in the northwestern part of the district are irregu- 

 larly dissected by rather close-spaced, early mature valleys, of which the 

 larger ones, 250 or 300 feet in depth, trend southwestward as if eroded 

 by superposed streams that were originally consequent on a former sand- 

 stone cover, while the smaller ones are for the most part of insequent 

 habit. The red sandstone ridges rise 200 or 300 feet over the broad, late 

 mature subsequent valleys that follow the intercalated shale belts ; here 

 the drainage is well adjusted to the structure. The gently rolling surf are 

 of the crystalline uplands and the even crestlines of the sandstone ridges, 

 taken with the equable altitude of two east-west dikes, one of which 

 crosses the fault line, suggest that, since the tilting and faulting, the 

 whole district has been eroded to a peneplain, again broadly uplifted sev- 



