230 



the dip were, say, a southwest dip, then the southwaru airection of the 

 dip would be revealed by wet surfaces on the north side of outcrops, 

 while the westward dip would be revealed by moisture on the east side 

 of exposures. 



Springs. — Such conditions as have been outlined above often result 

 in the formation of springs. Sometimes a chain of springs is formed 



Fig. 2. The case of a stream cutting through strata approximately at right angles 

 to the dipping beds. Springs will be formed at the contact of porous and Impervious 

 layers on the left bank of the stream. 



Fig. 3. Showing ci-oss-section of a partly disected anticline. Springs may be formed 

 in the valleys on each side of the axis at the points of contact of pervious and imper- 

 vious layers. 



along an exposure on its down-dip side. The essential conditions for a 

 spring, such as a porous layer overlying an impervious one, must be 

 present. Springs are of especial value as indicia in cases of concealed 

 outcrop. Even if the bed-rock be concealed by mantle rock, springs often 

 break forth at the point of contact of the pervious and impervious beds 

 and by observing the position of these along the valley walls of cross- 

 cutting streams, as in the case of wet surfaces, the direction of dip 

 may be determined. 



