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(a)
f
(b)
Figure 2.11.
Sheet fractures associated with faults and overthrusting planes (“f ”) exposed (a) in the Rock of
Ages Quarry, Barre, Vermont, in November, 1965. (b) O Pindo, Galicia, Spain.
material is involved. In such structures, sheet jointing is construed as due to vertical movement
and the development of radial stress, rather than to lateral compression; sheet jointing is caused
by radial stretching introduced during uplift. A number of objections can be levelled against the
hypothesis as a general explanation. For example, if denser material were displaced, then the
intruded mass would surely be in compression. Sheet structure occurs in sedimentary and vol-
canic rocks which have not been subjected to doming, and, if the sheeting joints are stretching
planes, it is difficult to explain the preservation of inselbergs as well as the other field evidence
indicative of compression.
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It has also been suggested that sheeting joints may be an expression of lateral compression which
results not only in faulting, but also in shearing. After the erosional removal of superincumbent
 
 
 
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