undermassn.

Etymology: under- prefix¹ 2b(c).Previous versions of the OED give the stress as: ˈundermass.

Geology.

An older, deformed body of rock overlain by younger, undeformed strata.

ΘΚΠ

the world > the earth > structure of the earth > constituent materials > rock > [noun] > rock at low or lowest level

bottom rock1810

undermass1942

1966 Bull. Geol. Soc. Amer. 77 707 The folds and faults mapped at the surface [near the San Andreas fault] are attributed to raft tectonics whereby a passive surficial plate is deformed as it rides coupled to a moving undermass.]

1942 O. D. von Engeln Geomorphol. ix. 168 The geomorphic significance of the abrupt, commonly marked in kind, transition between the materials above and below a plane of angular unconformity is indicated by the introduction of the terms cover mass and undermass.

1956 D. L. Linton Sheffield ii. 35 We..interpret it as the product of the cycle(s) of erosion which stripped away the presumed chalk cover, removed some hundreds of feet of the undermass, and saw the first group of adjustments of the superimposed streams to the underlying structures.

This entry has not yet been fully updated (first published 1986; most recently modified version published online June 2019).

单词	undermass
释义	undermassn. Etymology: under- prefix¹ 2b(c).Previous versions of the OED give the stress as: ˈundermass. Geology. An older, deformed body of rock overlain by younger, undeformed strata. ΘΚΠ the world > the earth > structure of the earth > constituent materials > rock > [noun] > rock at low or lowest level bottom rock1810 undermass1942 1966 Bull. Geol. Soc. Amer. 77 707 The folds and faults mapped at the surface [near the San Andreas fault] are attributed to raft tectonics whereby a passive surficial plate is deformed as it rides coupled to a moving undermass.] 1942 O. D. von Engeln Geomorphol. ix. 168 The geomorphic significance of the abrupt, commonly marked in kind, transition between the materials above and below a plane of angular unconformity is indicated by the introduction of the terms cover mass and undermass. 1956 D. L. Linton Sheffield ii. 35 We..interpret it as the product of the cycle(s) of erosion which stripped away the presumed chalk cover, removed some hundreds of feet of the undermass, and saw the first group of adjustments of the superimposed streams to the underlying structures. This entry has not yet been fully updated (first published 1986; most recently modified version published online June 2019). < n.1942
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