Bulletin of the National Speleological Society - ISSN 0146-9517
Volume 22 Part 1: 43-53 - January 1960
A publication of the National Speleological Society
Terminations of Passages
in Appalachian Caves as Evidence for a Shallow Phreatic Origin
William B. White
Considerable controversy exists between advocates of the deep phreatic theory of cave origin of Davis and Bretz and advocates of the shallow phreatic theory of Davies and Sweeting. The deep phreatic theory predicts cavern enlargement along any open conduit in a lithologically suitable bed without regard to depth below the water table. The shallow phreatic theory predicts solution only in a limited zone just belwo the water table. The latter theory was supported by evidence found in the examination of about 25 caves in the Appalachian Mountains.
Caves with maze patterns have apparently formed by slow phreatic flow along a soluble bed. In flat-lying limestone, caves with this pattern may have considerable area, but in strata of medium dip, passages on the updip and downdip sides terminate abruptly. Hence solution is limited to a narrow zone, even though the soluble bed continues in both directions. Several caves in nearly vertical limestone have been examined. In none of these had solution extended any distance along the bedding in a vertical direction, even thorugh a favorable bed and good parting existed in that direction. Instead the caves are limited to a nearly horizontal zone. Cross sections of caves in steeply dipping limestone show that the passages tend to be elongated along layers of good solubility. In the updip direction the cross seciton narrows and pinches out. In the few caves where the cross section can be traced downdip, the same thing is observed.
These data show that caves tend to maintain their horizontal pattern in spite of strcuture and lithology. The position of the water table is apparently the dominant controlling factor; structure and lithology seem merely to modif the ground plan and passage cross section.
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