136 W. H. HOBBS REPEATING PATTERNS IN STRUCTURE OF LAND 



In the semi-arid regions, where likewise the mat of vegetable material 



Figure 13. — Drainage Map of the RedfieM Quadrangle, South Dakota 



Showing control of drainage network by a fracture system. (After U. S. Geological 



Survey) 



is lacking, and particularly on elevated plateaus where frost work is likely 

 to be effective, a strong control of the drainage directions is to be looked 



