George R. MacKay (or Mackay, McKay) resided in East London during most or all of his adult life. He served in the Engineer's Department of the Cape civil service from March 1854 to August 1857, when he was transferred to British Kaffraria (the region between the Kei and Keiskamma Rivers, including East London) as superintendent of public works (acting to January 1862). In May 1872 he became clerk of works to the East London harbour. Towards the end of his career, in April 1887, he became assistant to G.F. Tippett, resident engineer of the harbour works. He appears to have retired in 1890, for in December that year he was re-appointed, as keeper of the lock-up at Post Retief, some 30 km north of Fort Beaufort. From January 1893 he was the gaoler at nearby Stockenstroom, on the Kat River, for a few years.
MacKay was a self-taught geologist with a life-long interest in fossils and prehistoric stone artefacts, and an early collector of both in the eastern Cape. Identified as "Mr Mackie of East London" he was elected an honorary member of the Albany Natural History Society on 9 October 1867. By that time he had constructed a model of the mouth of the Buffalo River and adjacent banks and had collected specimens illustrating the geological strata of the area covered by his model. One of these specimens was the fragmented skull of a mammal-like reptile. The specimens were exhibited at the Paris Exhibition of 1867, after which the skull was submitted to the Geological Society of London. It was studied by T.H. Huxley*, who described it, with notes by MacKay, in the Geological Magazine (1868). It was named Pristerodon mackayi after the discoverer and is preserved in the British Museum (Natural History) as the holotype of the species. Some further notes by MacKay on fossils from the Buffalo River were published in the same volume.
In February 1867 he presented, via R.N. Rubidge*, two Dicynodon fossils and some geological specimens to the Port Elizabeth Natural History Society (1866-1867), followed during the next few months by a sample of recent shelly limestone, artefacts on sandstone, and further mammal-like reptile fossils. One of the fossils was named Rubidgea kayi in his honour, but was later renamed. The next year he accompanied H.W. Piers* to Fort Grey, some 15 km west of East London, where they studied a deposit containing much fossilised wood, which appeared to have been eroded out of older strata and redeposited. By this time MacKay had presented a "valuable collection of fossil remains of unknown animals" (Piers, 1868a, p. 218) to Sir R.J. Murchison at the London School of Mines. In 1871 he donated a fragmented fossil skull from the Dicynodon beds of East London to the Albany Museum, Grahamstown. It appeared to be a new species and was named Oudenodon raniceps by Sir Richard Owen*, but the name later became a synonym for Pristerodon mackayi. He presented further fossils to the Albany Museum in 1884.
MacKay's main contribution to geology, "Notes on the geology of the coast between the Fish and Juja Rivers, South Africa", was read on his behalf before the South African Philosophical Society, Cape Town, on 26 March 1884 by John G. Gamble* and published both in the society's Transactions (Vol. 4, pp. 1-6) and as a pamphlet (Cape Town, 1887). When the South African Geological Association was founded in Grahamstown in June 1888 MacKay was elected a member of its committee.
In 1897 MacKay mentioned that he had first collected pottery from a shell midden at the junction of the Quigney and Buffalo Rivers as early as 1857. This is even earlier than the first recognition of local prehistoric artefacts by the pioneer collector Colonel T.H. Bowker*. However, there is no evidence that MacKay was the first to recognise South African stone artefacts as products of human activity, though he was recognised as an important early figure in local archaeology by local writers on prehistory such as Prof Langham Dale* (1870), A.P. Hillier* (1886) and Justice Sydney T. Jones* (1893). Hillier mentioned that MacKay's guidance had enabled him to collect artefacts himseld, and described MacKay as "one of those silent workers", reflecting the fact that he did not publish his finds during the early years. By 1870 he had compiled a list of 11 places or regions, most in the Eastern Cape, where stone artefacts had been found, with brief descriptions. The list was published by Dale in the Cape Monthly Magazine that year. Some artefacts collected by MacKay in the East London area were included in donations to the British Museum (Natural History) by Dale in 1872, and later by J. Lubbock in 1916.
At the second meeting of the South African Geological Association in January 1889 MacKay read a paper on "The antiquity of man as evidenced by certain prehistoric remains at East London", a lengthy summary of which was published months later in the Grahamstown Journal. He described, among others, the discovery of a large number of stone artefacts at a depth of about a meter, that were exposed by a railway cutting at East London; pottery, bored stones and other artefacts deposited on the edge of a former muddy plain but now covered by a hillock of soil near the East London Botanic Garden; and artefacts and bones found deep in fossilised dunes along the Eastern Cape coast - all providing evidence of the antiquity of human activity. The paper demonstrates MacKay's original application of geological observations to date archaeological remains.
MacKay was still scientifically active in 1897, when he presented a human skull, found during excavations in or near East London harbour, to Albany Museum. That same year a paper, "Evidence on the antiquity of man in East London, Cape Colony, with a note on the castor oil plant", was published under his name in Natural Science (Vol. 11, pp. 334-336). It was based on his 1889 paper and was submitted to the editor of the journal by Dr S. Schonland*.