104 OUTLINES OF HKLD-GEOLOGY 



possible kind, considerable practice and skill may l>e 

 needed to follow the exposed edges or outcrops of the 



. and to delineate them accurately, and at the 

 time artistically, upon a map. The accompanying draw 

 ings (Fig. 24) may serve to illustrate how very tortuous t he- 

 outcrops of perfectly horizontal beds may be, should the 

 ground be much varied in outline, and especially if it he 

 diversified with wide and deep valleys. In the upper- 

 most map (A) a representation is given of hori, 

 rocks deeply trenched by valleys and ravines. In the 

 lower map (B) the inequalities of the ground are much 

 less, yet even in such a gently undulating district the out- 

 crops of horizontal strata may evidently run in remarkably 

 sinuous lines. In a high plateau region of hori/.ontal strata 

 which has been deeply trenched by ravines and where end- 

 less outliers have been left isolated, the mapping even of 

 this simple structure may involve infinite labour from the 

 multiplicity of lines of outcrop that have been exposed by 

 the denudation. But if the mapping be done carefully and 

 accurately it may serve as a model from which the topo- 

 graphy of the country will be at once grasped by the eye. 

 The singularly dissected plateau-regions of South Africa 

 furnish admirable illustrations of this kind of geological 

 structure and resulting scenery. 



I have used the word artistic with reference to the 

 tracing of geological boundary-lines, and have done so 

 advisedly. Where the rocks are all visible, the observer 

 has only to follow nature, and the more faithfully he does so, 

 the more graceful will his lines probably be. The curves 

 produced by denudation, though often complex, are never 

 awkward and inharmonious. Where the rocks are not 



