ix OUTCROP AND STR I 113 



raighl and parallel strips of clay, lime 

 tones, and sandy rocks. But instead of being a flat, 

 the country undulates ; hence a series of gently inclined 

 rocks of various degrees of durability necessarily gives 



ersified set of outcrops. No better illustration 

 could be studied of the difference between outcrop 

 and K I of the marked influence even of small 



ridges and hollows and shallow valleys upon the outcrop 



ita, where the angle of dip is low. The main facts 



to be expressed upon the map of such a tract of country 



^ follow each other in a certain 



cgion in a certain direction. Of 



course we might record these (acts by simply drawing 

 straight parallel strips across each marking the 



i and relative breadth of one of the forma- 

 tions. This was the way in which the old geological 

 maps on a small scale were constructed, and indeed when 

 the scale is minute, no other mode of repres* 

 possible. The map of Kngland and Wales in Bake 

 GtoloQ, even so late as the edition of 1838, may serve 

 as an example. But by such a style of mapping we 



\ lose, as I 'liable 



es of a geological map the relation between the 



al form of the ground and the nature and grouping 

 of the rex ks in-low, thai is, between scenery and geological 

 structure. It may readily be believed that this is too 

 important a relation to be ignored without great disad- 

 vantage when the scale of the map at all permits it to be 

 expressed. Besides, the omission deprives the map of 

 the chief feature by which the work of a skilled and 



observer is distinguished, whose eye and hand 



