subsoil

n. 下层土,底土

Permanently frozen subsoil, occurring throughout the Polar Regions and locally in perennially frigid areas.

永冻土永久冰冻的下层土壤，出现在整个北极地区和部分长期寒冷的地区

A specific layer of soil or subsoil in a vertical cross section of land.

地层，岩层处于土地的垂直横截面中的某一具体土层或次土层