J.L. Cairncross (probably James Lilburne Cairncross) resided in Prince Albert in 1905 when he found hitherto unknown fossil reptile remains in rocks of the Ecca Group. He donated the fossils to the South African Museum, where Robert Broom* had just been appointed as honorary keeper of vertebrate palaeontology. Broom described the find in his annual report as an important discovery. Cairncross was one of many fossil collectors recruited by Broom around this time, and he must have been acquainted with Rev. J.H. Whaits*, who collected in the same area. In 1906 he again sent in "interesting vertebrate fossils", followed in 1907 by some fossils from the Bokkeveld Group, and some plant remains from the Enon beds of Oudtshoorn. In 1908 most interest in his donations was generated by an Early Cretaceous fossil fern of the genus Cladophlebis, from the Uitenhage beds. He also sent some shells from the Bokkeveld Group.
In 1911 Cairncross, then residing at Oudtshoorn, presented stone artefacts, perforated stones, and various Bushman implements and ornaments to the McGregor Museum in Kimberley.
James Lilburne Cairncross was married to Eliza Sarah Bobbins.