Sentence:  Oil-shales are often the last relics of a former impregnation with petroleum; they are associated with phenomena—such as the intrusive asphaltites or <WSD>manjacks</WSD>—common to petroliferous regions, but in many cases the parent oilfields, the sources of the former impregnation, are things of the past. 
Meaning of the word marked with <WSD> tags:  A form of bitumen-rich asphalt found in Barbados and Trinidad.