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Certain Indicia of Dip in Rocks. 



William N. Logan — Indiana University. 



The object of this paper is to bring together certain indications of 

 dip and the direction of dip in rocks which the writer has observed in 

 his field work. All of these indicia have been noted doubtless by other 

 observers of geological conditions. However, they are brought to- 

 gether here in the hope that the collection may be of assistance to 

 students of structural problems in geology. 



Fig. 1. Cross-section of strata, showing dipping beds with a gulch approximately 

 at right angles to the dip. Right surface of rocks in gulch damp, left surface, dry. 



Wet or Damp Surfaces. — In the case of an outcrop extending ap- 

 proximately at right angles to the dip of the beds the exposed surface 

 of the rocks on the lower side of the dipping beds may be bathed in 

 moisture. The presence of the moisture is due to the seepage of water 

 from the porous layers in the rocks. Such seepage can take place only 

 under certain conditions of humidity and would not be noticeable in an 

 arid region. If the outcrop is in a railroad cut or in a stream with 

 precipitous banks the outcrop on the opposite side from the damp sur- 

 face will be dry because the water is conducted away from its surface, 

 instead of toward it. The conditions are illustrated in the following 

 diagram in which the shaded side of the cut on the down-dip side is 

 kept moist by water flowing along the bedding planes and through 

 porous layers, while the surface of the rocks on the opposite side of the 

 cut is dry because the water is conducted away from the exposure. If 



