CHARACTERISTICS OF JOINTS AND FAULTS 485 



the presence of an isolated anticline upon the present theory of folding , 

 and it is believed, as a result of field observation, that individual faults 

 unrelated to other planes of dislocation seldom occur. In all districts 

 where they have been studied carefully a tendency of faults to appear 

 like joints within essentially parallel series has been remarked. Like- 

 wise there has been observed a more or less marked tendency of the 

 minor faults to be spaced within such a series in approximation to uni- 

 formity, and this property, so characteristic of the joints with which they 

 are genetically connected, is one demanded by our theory of their origin 

 through regional compression, and one which is duplicated in the faults 

 produced artificially by the compression of an elastic body such as glass. 

 Additional properties of joint structures which may be inferred to be 

 also common to faults are that in regions which since their formation 

 have been little disturbed, the joint planes stand near the vertical, and 

 in their network two dominating series are generally found to be approxi- 

 mately normal to each other. 



CONCLUSIONS FROM STUDY OF SOUTHWESTERN NEW ENGLAND 



What is believed to be an important result of the study of the south- 

 western New England area is that lines of dislocation, while maintaining 

 often with great fidelity a definite direction, do so in part along a plane 

 whose course is the direction of the dislocation as a whole, but more 



Figure 1. — Diagram to Illustrate the Composite Nature of Lines of Dislocation. 



largely along other planes which may make considerable angles with it, 

 the course being here a series of zigzags. In these zigzags there may be 

 recognized several definite recurrent directions, as well as several differing 

 orders of magnitude, the lowest order having the joint planes for its 

 elements (see figure 1). 



TYPES OF EARTH LINEAMENTS 



The more important lineaments* of the earth physiognomy may be de- 

 scribed as (1) crests of ridges or the boundaries of elevated areas, (2) the 

 drainage lines, (3) coast lines, and (4) boundary lines of geologic forma- 

 tions, of petrographic rock types, or of lines of outcrops. Under the 



* It will be noted that the lineaments to which we have referred are not the equivalent of the 

 " tektonische Linien " of German writers. The latter are in most, if not in all, cases regarded as 

 lines of displacement. While believing that the greater number of rectilinear features have their 

 origin either in planes of jointing or in faulting, there appears to be no advantage, but serious 

 disadvantage, in giving this implication to the term. The term as here used is nothing more 

 than a generally rectilinear earth feature. 



