1. One of two or more simple substances forming the extreme ends of a solid solution series, e.g. albite (NaAlSi3O8) is one end member, and anorthite (CaAl2Si2O8) the other end-member, in the plagioclase series.
2. In palaeontology, one of the two distinct forms between which gradual variation occurs.
"end-member." A Dictionary of Earth Sciences. . Encyclopedia.com. (January 18, 2019). https://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/end-member
"end-member." A Dictionary of Earth Sciences. . Retrieved January 18, 2019 from Encyclopedia.com: https://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/end-member