These layers are called strata and a single layer is called a stratum.
这些岩层被称作地层(strata)(stratum的复数形式), 单个岩层称为stratum。
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"When we are in the bath and we have been there for a while the stratum corneum [outer] layer of our skin expands," says Evans. "This causes wrinkles and means our fingerprints will be enlarged also."
"The new soccer centre emerges from the park's artificial topography as a layer of mineral stratum recalling the geological nature of the site," said the architects.