From Longman Dictionary of Contemporary Englishsubsoilsub‧soil /ˈsʌbsɔɪl/ noun [uncountable] HEGTASthe layer of soil between the ground’s surface and the lower layer of hard rock
Examples from the Corpus
subsoil• The type of subsoil upon which the foundations are built is a very influential factor.• Deep ploughing puts subsoil on top and buries the living topsoil below the optimum depth.• Downtown businesses operated sump pumps as the subsoil water level rose.• Pierry derives its name from a stratum of flint in the subsoil which reputedly gives its wine a marked flinty taste.• Below this is the subsoil which is relatively inert.• Settlement is an inevitable movement which occurs due to the weight of the building upon the subsoil.• They were tempted by the vast underground riches of a country whose subsoil has been described as a geological scandal. 