170 EARTH FEATURES AND THEIR MEANING 



line with a simple curve convex toward the sky (Fig. 176). In 

 this stage large sections of the original plateau remain, though 

 cut into small areas by the ex- 

 tensions of the tributary valleys. 

 The maturely dissected up- 

 land. Continued ramifications 

 by the rivers eventually divide 

 the entire upland area into sep- 

 FIG. 176. -v-shaped valley with well- arated parts, and the rounding 



rounded shoulders characteristic of of the shoulders of valleys pro- 

 the stage of adolescence. Allegheny ceedg simultaneously until of the 

 plateau in West Virginia. . . . , , ., 



original upland no easily recog- 

 nizable compartments are to be found. Where before were flat 

 hilltops are now ridges or watersheds, the well-known divides. 

 The upland is now said to be completely dissected or to have 

 arrived at maturity. The streams are still vigorous, for they 

 make the full descent from the upland level to base level, and 



yet a critical turning point of ^ ^^ 



their history has been reached, 

 and from now on they are to 

 show a steady falling off in effi- 

 ciency as sculpturing agents. 



Viewed from one of the hill- FIG. 177. View of a maturely dissected 

 tops, the landscape Of this Stage upland from one of its hilltops, Kla- 



bears a marked resemblance to 



a sea in which the numberless 



divides are the crests of billows, and these, as distance reduces 



their importance in the landscape, fade away into the even line 



of the horizon (Fig. 177). 



The Hogarthian line of beauty. Since the youthful stage of 

 the upland, when the lines of its landscape were straight, its 

 character rugged, and its rivers wild and turbulent, there has 

 been effected a complete transformation. The only straight line 

 to be seen is the distant horizon, for the landscape is now molded 

 in softened outlines, among which there is a repeated recurrence 

 of the line of beauty made famous by Hogarth in his " Analysis of 

 Beauty." As well known to all art students, this is a sinuous 

 line of reversed or double curvature a curve which passes 

 insensibly at a point of inflection from convex to concave (Fig. 



math Mountains, California (after a 

 photograph by Fairbanks). 



