VARIED EXPRESSION OF LINEAMENTS 143 



since the curvature of folds in the plan is a direct measure of the plunging 

 character of the crest or trough lines. 



OBSCURE PATTERNS REVEALED IN STUDIES OP THE JOINT SYSTEM 



Whenever the relief pattern due to control by a fracture system is too 

 obscure to be directly read from the map, the evidence for partial control 

 in the orientation of waterways may often be found by comparing the 

 directions of master joints within the rocks of the district with the direc- 

 tions of the neighboring stream-courses. Studies of this character have 

 been carried out, among others, by Harder,^^ Lind,^^ and the writer.^^ 



The DIVIDING Lines of Eelief Patterns — Lineaments 



THE VARIED EXPRESSION OF LINEAMENTS 



We have seen that the repeating patterns of the relief, whether ex- 

 pressed in topographic or in hydrographic maps, are divided on lines 

 which, for limited distances at least, are essentially rectilinear. These 

 lines may be expressed in shores, fjords, valleys, escarpments, sags, or in 



n > t e 



G S t o 



Figure 20. — Schematic Diagram indicating the composite Expression of a Lineament 



the equally definite stream lines. Generally they are expressed in one 

 portion in one way and in another portion by a different feature — they 

 are essentially composite in their expression. Often where the drainage 

 network alone does not clearly reveal the pattern or the dividing lines, a 

 supplementary study of the topographic or geologic map may do so (see 

 figure 20). Thus a waterway may be continued by a sag or trench not 

 brought out in the hydrography, or by a line of waterfalls in transversely 

 flowing streams, or, lastly, by a significant boundary between geological 

 formations. However expressed, these approximately right lines in the 



1' E. C. Harder : The joint system in the rocks of southwestern Wisconsin and its 

 relation to the drainage networl?. Bulletin of the University of Wisconsin, Scientific 

 Series, vol. 3, No. 5, 1906, pp. 207-246, pis. 1-10. 



1^ J. G. Lind : Geologische Untersuchungen der Beziehungen zwischen Gesteinspalten, 

 der Tektonik und dem hydrographischen Netz des Gebirges bei Heidelberg (mit einer 

 karte). Verh. d. naturh. medicin. Vereins zu Heidelberg, N. F., vol. 11, 1910, pp. 7-45. 



1" W. H. Hobhs : Examples of .ioint controlled drainage from Wisconsin and New York. 

 Journal of Geology, vol. 13, 1905, pp. 363-374. 



