234 



containing minerals in solution. These minerals left behind fill the 

 pores of the rock and unite the individual grains of the rock, thus hard- 

 ening the surface. The rocks on the opposite side of the cut may lack 

 this degree of induration because, since the dip is away from the out- 

 crop, the greater part of the water is drained away from the surface 

 and the amount evaporated at this point is small. 



Fig. 7. Cross-section and horizontal section of strata containinjr sink holes, 

 longer axis of holes parallel to the direction of dip. 



Note 



Deposition of Sediment. — On the surfaces of layers of hard rock 

 which are inclined either in quarries or stream beds the deposition of 

 sediment may indicate the direction of dip. The thicker accumulation 

 of sediment will occur in the direction of the dip. In the case of quarry 

 floors which are formed on the stratification planes the distribution of 

 rock dust and other forms of debris by running water will reveal the 

 direction of the dip. 



Distribution of Vegetation. — In inclined beds which outcrop, vegeta- 

 tion is sometimes more abundant on the side of the outcrop opposite 

 the direction of dip. This greater abundance when it does occur is due 

 to the increased amount of moisture and its almost constant supply to 

 the surface of the outcrop through the porous layers which are draining 

 down the dip. 



