sub·stra·tum
noun/ˈsʌbstrɑːtəm/
/ˈsʌbstreɪtəm/
(plural substrata
(specialist)/ˈsʌbstrɑːtə/
/ˈsʌbstreɪtə/
)- a layer of something, especially rock or soil, that is below another layer
（尤指岩石或土壤的）下卧层；底土层 - a substratum of clay
粘土基质 - the substrata of society
社会底层
Word Originmid 17th cent.: modern Latin, neuter past participle (used as a noun) of Latin substernere, from sub- ‘below’ + sternere ‘strew’. Compare with stratum. - a substratum of clay