COLLAPSE OF RECENT BEDS AT STAUNTON 4! 



tation." In a limestone region the movement of underground waters 

 following the line of least resistance, is controlled almost entirely 

 by joint planes and bedding planes. Where the rocks are tilted 

 only moderately, or not at all, the joint planes generally exercise by 

 far the greater influence on the movement of the underground waters 

 and consequently upon the direction of subterranean channels. 

 If, however, the beds are highly inclined or vertical, the surface 

 waters have a strong tendency to descend along bedding planes, 

 and joints have less influence in directing their movement. The 

 efficiency of bedding planes in controlling the movement of under- 

 ground waters is clearly stated as follows by Bain: "Bedding 

 planes between strata are natural division planes and under the 

 slightest stress or the action of solutions they afford openings of 

 even greater extent than fault planes." 5 



When the joints intersect at various angles, as is frequently the 

 case, the courses of the underground streams controlled by them 

 will be irregular. Where the joints are uniform in direction the 

 underground streams are likely to show a corresponding uniformity. 

 This is illustrated by the caves in the Mitchell limestone in Indiana 

 and Kentucky according to Mr. F. C. Greene. In this formation 

 the joints have a general east and west and north and south direc- 

 tion. "Thus young caves and many which are older follow approx- 

 imately straight north and south and east and west lines and have 

 right-angled turns." 6 



When, however, the direction of the movement of underground 

 waters is controlled by nearly vertical bedding planes the horizon- 

 tal flow will follow the direction of strike, and the resulting sub- 

 terranean channels will necessarily follow in the main the strike 

 of the beds. The subterranean channel disclosed by the caving 

 marl and clay beds at Staunton illustrates this type of stream. Exam- 

 ination of the strike and dip of the rocks in all directions within 

 a radius of a few hundred yards from the caved area showed the 

 beds to be inclined everywhere at a high angle, usually 75 to 90. 

 (PL I.) The strike within the limits of the city has a uniform direct- 



5 Preliminary Report on the lead and zinc deposits of the Ozark region; H. F. Bain, 

 C. R. Van Hise and G. J. Adams; 22nd Ann. Rept. U. S. Geol. Surv., Pt. II, 1901, 

 P- 97- 



6 Proc. Ind. Acad. Sci., 1908, p. 178. 



