With the exception
of rock shelters, the caves of Maryland show a tendency to develop along
joints. Faults, cleavages, or fractures other than joints are apparently
not significant in controlling the direction of passages in solution-type
caves. In most caves one set of joints exerts major control over the pattern
with the larger passages developed along them, and subordinate side passages
follow the secondary joints.
In flat-lying limestones in Garrett County,
caves are simple in pattern. Generally, one main passage is developed
that follows a major set of joints with occasional offsets along subordinate
joints. Multiple levels are confined to local sections of caves and are
connected by vertical cliffs or shafts. Passages slope uniformly but show
no consistent relation to the dip of the rocks.
developed at joint intersection
In folded strata,
where caves lie on the flanks of folds, passages develop as fissure-like
openings along steeply inclined joint planes. The passages vary from a
few feet to over 100 feet high and consist of several parallel openings.
Except in Twiggs Cave, the passages are offset along the dip where they
occur in more than one level. In Twiggs Cave the joint control is so dominant
that levels are not offset but are developed one above the other.
near the crests of anticlines, like Revells Cave and Crystal Grottoes,
have a maze of interlacing passages equally developed along two or more
sets of joints. This results in a plan resembling city blocks.
With the exception of Sand Cave and Devils
Den, bedding exerts little control in cavern development in Maryland except
to modify the cross-sectional shape of some passages. In Sand Cave the
bedding determines the extent of the cave, and joints tend to modify the
shape of the walls, but are otherwise unimportant in controlling the pattern.
In Devils Den the bedding determines the direction of the major passages.
It has been observed that a predominance
of Maryland caves exhibit a marked horizontal nature and extent. Very
few have more than 100 feet of vertical relief. Many have sloping passages
but for the most part remain on one plane. The control of pattern by the
strike of the rocks is not constant. At high dip, however, strike-oriented
patterns are common but by no means the rule. In flatter limestones, there
is no preferred pattern (e.g. Crabtree Cave).
These views are further substantiated by
Barr (1961), who classified Tennessee caves into two major types according
to inclination of the beds. He proposed the terms Allegheny and Appalachian
to designate these types. Allegheny type caves are developed in strata
of relatively low dip (e.g. Garrett County). The floors and ceilings tend
to be horizontal except where secondarily modified by fill, breakdown,
and domepit. Major passages tend to follow the dip, with patterns often
being complex and different levels superimposed.
type caves appear in steeply or moderately inclined beds and are the predominant
pattern in the Appalachian Valley (Washington and Allegany Counties).
The floors and ceiling of different levels are not superimposed, as a
rule, but tend to occur down-dip from, and usually parallel to, other
levels. Devils Hole Cave in Allegany County is a good example of this.
In summary it may be said that the caves
of the Appalachian Ridge and Valley province are typically single conduit
type passages parallel to the ridges, with large lateral extents being
rare. The limestones do not have protective cap rocks, so the caves are
subject to relatively easy truncation and collapse processes. The limestones
of the interior plateaus, in contrast, are nearly flat-lying and occur
often under sandstone or shale-capped ridges. These caves are related
to much larger drainage basins, often by as much as a factor of 10 (Poulson
and White, 1969), than those caves in the Appalachians and have a relatively
larger lateral extent.
-Caves of Maryland)