COLLAPSE OF RECENT BEDS AT STAUNTON 47 



well, as supposed by Mr. Yost, there should have been no 

 such difficulty as is reported in pumping from the well after 

 the caving ceased. This rise of water in the "cave-in" doubt- 

 less represents the original level of ground water previous to 

 the caving. If this is true it follows that the roof of the cavern 

 received a certain amount of support from the water which filled it 

 previous to the caving. If we suppose the normal development of 

 the cavern to have reached the point where the strength of the 

 materials comprising its roof made them barely self-sustaining, 

 the withdrawal of this hydrostatic support, however slight it may 

 have been, combined with the rapid subsurface erosion of the 

 marl which may have resulted, would have served as a trigger 

 to start the collapse of the roof. Caving as a probable result of 

 the withdrawal of such support is not only a theoretic but an ob- 

 served fact in some mining districts, as will be seen from the 

 following quotation from Smith and Siebenthal. 9 



"Where caverns are below the ground-water level and full of water 

 the water helps support the weight of the roof. Where the balance is 

 nicely adjusted and the roof is only just self-sustaining, ifthewaterbe 

 withdrawn the cave will collapse. In a number of cases in the Joplin 

 district such collapsing has followed the lowering of the ground-water 

 level by pumping in the deeper mines. Without doubt many "natural 

 caves" have in the geologic past resulted from the draining of caverns 

 by elevation of the land and other causes, and have developed into closed 

 valleys." 



The above statement is substantiated by Bain 10 who cites in the 

 following quotation specific instances where collapse has resulted 

 from the withdrawal of hydrostatic support in the lead and zinc 

 region of southwestern Missouri. 



" An interesting phenomenon of the Joplin caves is the fact that in them 

 the weight of the roof is occasionally partly supported by the hydro- 

 static pressure of the water When the water is pumped out the roof may 

 fall in. This occurred at the Budweiser mine at Tuckahoe. Near the 



9 Smith and Siebenthal; Joplin District Folio Missouri-Kansas; U. S. Geol. Surv., 

 Bull. 148, 1907, p. 8. 



10 Preliminary report on the lead and zinc deposits of the Ozark region, H. F. Bain. 

 With an introduction by C. R. Van Hise and chapters on the physiography and geol- 

 ogy by George I. Adams, 22d Ann. Rep. Director U. S. Geol. Surv., Pt. IT, 1901, p. no. 



