STRUCTURAL CONTROL OF NETWORKS 



135 



within the rock are able to exert a control over the location of water- 

 ways. We have already emphasized the fact that in high latitudes, where 

 there is generally scant cover of vegetation and where frost work is the 

 dominant weathering process, such control will be at a maximum and 

 repeating relief patterns will in consequence be given a strong expression. 

 In western Greenland, where the fjords and valleys appear as definitely 

 0] iented right lines on the map, it has been shown that outlet glaciers 



Figure 12. — Rain-sculpturing controlled ty Joints 

 Coast of southern California. (After a photograph by Fairbanlis) 



from the inland ice actually clean out the talus deposits which collect in 

 the bottom of clefts as a result of frost action upon their walls. These 

 clefts, in consequence, are extremely narrow canyons which flare at both 

 the top and bottom, as is shown in figure 11.^° "They are," says von 

 Drygalski, "too little developed for running water to have had a part in 

 forming them.'^ 



" E. von Drygalski : Gr5nland-ExpeditIon der Gesellschaft fiir Erdkunde zu Berlin 

 1891-1893, pp. .S6-43, pi. 7. 



