Impregnation

Earths and alkalies are simply metallic oxides; whilst a farther impregnation of these substances with oxygen produces an acid....

Oil-shales are often the last relics of a former impregnation with petroleum; they are associated with phenomena—such as the intrusive asphaltites or manjacks—common to petroliferous regions, but in many cases the parent oilfields, the sources of the former impregnation, are things of the past.