Jackson, John Semple (1920–91), geologist and environmentalist, was born 21 February 1920 in Dublin, fifth child among four sons and two daughters of Francis Robert Jackson, managing director of several businesses in Athy, Co. Kildare, and his wife Annie Elizabeth, youngest daughter of Robert St John, jeweller, from Nenagh, Co. Tipperary. John's mother died (1931) when he was 10 years old. His father married her sister, Harriet (‘Tot’) Semple, who had previously come to live in the house on the death of her husband, the Rev. John Semple, but there were no children from this second marriage.
His childhood was spent at Farmhill, Athy, Co. Kildare, where he was surrounded by a multitude of cousins. He went to the Model School, Athy, spending his secondary education (1934–40) at St Columba's College, Rathfarnham, Co. Dublin, where he enjoyed rugby. On leaving school he spent some time working in the family business and began studying architecture, passing the preliminary exam for ARIAI. He met his future wife, Sally (Mary Adina McCutcheon of Ballinasloe), at a dance in Alexandra College, Dublin (c.1941), where she was a pupil and friend of his cousin. In 1942 he was accepted for Oxford University, but he joined the RAF (1943) instead, training as a pilot in England and Miami, Oklahoma, USA. Sally joined the Women's Auxiliary Air Force soon after and trained as a radio mechanic; they managed to meet several times during the war. He returned to England and began training other pilots at Cambridge. Flying over the wide vistas of North America is said to have encouraged his interest in geology and landscape, and after the war he began studying natural science at TCD (1946), receiving the Edge prize (1949) and his BA (1950) in geology and zoology. Adept at burning the midnight oil, he also led an active student life and edited the magazine TCD. Sally returned to TCD in 1947 and began a degree in mental and moral philosophy (BA 1951) and on 6 November 1948 they eventually married at Holy Trinity church, Rathmines. They juggled the care of their first child (b. 1950), enabling each to attend lectures.
His first appointment (1951) was lecturer in the geology department, UCD, where he taught with enthusiasm. Palaeontology and stratigraphy were his main research interests and his detailed investigations of the carboniferous stratigraphy of Kingscourt, Co. Cavan, led to his Ph.D. (TCD 1955) and a paper in the RDS Scientific Proceedings. In 1957 he left UCD on his appointment as keeper of the Natural History Museum, Dublin. The museum offered a broad scope of activities, varying from the identification of fossils to stranded whales. However, administration and regular museum duties began to restrict his love of outdoor geological pursuits to the weekends. There was a saying in the family: ‘If your job interferes with your hobby, give up your job’. In 1968 he took a leap of faith in the burgeoning mining and quarrying industry by resigning his post, to become one of the few geological consultants in Ireland at that time. His extended brief included amenity and nature conservation and he has been described as the first environmental consultant in Ireland.
As well as providing advice to quarry owners and mining developers, he gave lectures on mining and engineering geology in TCD (1968–70) and UCG (1972–5), and was extension lecturer of the RDS and consultant palaeontologist to the Geological Survey of Ireland (1971–5). He lectured on environmental conservation to architecture students in Bolton St. College of Technology and contributed to conservation and mining broadcasts on radio and television. As a consultant he also worked for An Bord Failte and with David Webb (qv), A. E. J. Went (qv), and W. A. Watts, prepared a list of sites of scientific importance in Ireland (1963); he became a member of the two government working parties for the preparation of the inventories of outstanding landscapes and sites of scientific interest in Ireland, the latter a precursor to what are now Special Areas of Conservation (SACs) under EU legislation.
Some of his wide-ranging publications on geology, archaeology, nature, and environmental conservation are listed in Who's who, what's what and where in Ireland (1973), from the effects of draining bogs to prehistoric mining, but his most important body of detailed geological work is contained in copies of his company reports lodged with the GSI. The scope of his activities and breadth of knowledge, at a time of growing awareness of conservation issues in Ireland, led to numerous appointments on European, government, and semi-state advisory groups and committees, including the European committee for the conservation of nature and natural resources, and the RDS committee for science and its industrial application; he was also chairman of the editorial committee of the Irish Naturalists’ Journal and chairman of the advisory committee on the conservation of nature and amenity, An Foras Forbartha, which produced the national heritage report of 1964. He was a committed member of many societies: the RDS, Royal Zoological Society of Ireland, FGS (London), Geological Association (London), Irish Geological Association (of which he was a founder member and first president), Palaeontological Society, Geological Society of Yorkshire, Systematics Association, and most notably An Taisce, of which he was secretary (1964–6), chairman (1974–5), and president (1975–7).
A man with an enthusiastic zest for life and an effervescent sense of humour, he always took a great delight in sharing his knowledge and interests. He had many friends and it was difficult to draw a line between the professional and personal ones, among them Francis Synge, Frank Mitchell (qv), Ted Nevill of UCC, and Maj. R. F. Ruttledge (qv). He and his wife Sally had three boys and lived at Amygdale, Roebuck Road, Dundrum, before moving to St Columba's, Ballybrack, Co. Dublin (1956). She did a postgraduate degree in psychology (1965) at UCD and later worked as director of psychology for St Michael's House, Dublin (1966–74). They moved (1977) to Clondalkin, Dublin, where their son, Michael Lunn Jackson, began to set up his pottery business, Stoneware Jackson (later at Bennetsbridge, Co. Kilkenny). In 1988 they moved to Ardmanagh, Schull, Co. Cork. Even in retirement Jackson continued lecturing and investigating quarries and mines. Outside his work he enjoyed walking, mountain climbing, painting, and sketching. Wherever he lived, he became involved in the local church and societies: Clondalkin history society, the Mizen field club, Schull Development Association, and Schull Astronomical Society. He died suddenly 19 November 1991 in Killarney, Co. Kerry, and is buried in Altar graveyard, west Cork. The John S. Jackson Library, housed in the department of geology, UCC, contains his collection of 3,500 books, memoirs, journals, and maps, which he donated to the college in 1982 and 1987. In 1994 the RDS inaugurated the John Jackson Lecture series in his memory.