Hallissy, Timothy (1869–1958), geologist, was born 8 November 1869 in Garrycloyne, Blarney, Co. Cork, eldest among three sons and two daughters of John Hallissy, tenant farmer, and his first wife Mary Hallissy (née O'Shea). His father had tenancy (1855) of 186 acres, of which he got ownership in 1903, after the land act of that year. After his mother's death Hallissy and his sister went to live with his maternal grandmother, Elizabeth O'Shea, in Shandangan, near Macroom. His father remarried and had five more children with his second wife, Julia (née O' Callaghan). Timothy was educated first at Waterloo national school, Blarney, and then at Macroom. With the intention of studying medicine he entered QCC, but after an illness that required surgery on his face, he changed to science, graduating with a BA in chemistry and physiology (1893) from the Royal College of Science in Dublin. He taught agricultural science at Mount Bellew, Co. Galway, the college run by the Franciscan Brothers, and he became an associate of the Royal College of Science in agriculture (1904), where he also taught soil-physics. His agricultural background assisted him in his appointment as temporary professional assistant to the Geological Survey of Ireland (1905–6) to work on the new initiative by Grenville A. J. Cole (qv) to survey the soils of Ireland. Hallissy was reappointed for part of each year till 1908, when he was offered a permanent position as geologist with the survey. A new soils laboratory was set up in Hume St., Dublin, where soils were brought back from many parts of the country for detailed analysis. His knowledge of French and German helped him keep abreast of developments in soil science in Europe. From 1906 he worked with Henry Joseph Seymour (1876–1954) and James Robinson Kilroe (1848–1927) on the innovative soil map of the Ballyhaise agricultural station, Co. Cavan, previously the home of the Humphry family. The map was the first true soil map published (1910) in Ireland or Britain and the only one ever published by the GSI. It was another fifty years before the National Soil Survey of Ireland began publishing soil maps of Ireland.
After the work at Ballyhaise the focus of the survey's activities changed to more orthodox geology. Hallissy took this change on board and responded by buying geological books to augment his field experience. Although he took part in the Clare Island survey and assessed the island's drifts and soils, he was sole author of the geological section of the final publication (Clare Island Survey, ‘Geology’, RIA Proc., xxxi (1914), 1, pt 7). That same year (1914) he published a revision of the geology of Armagh, Fermanagh, and Monaghan (memoir of GSI, sheet 58). Later he contributed the complete section on agricultural geology for the Standard cyclopedia of modern agriculture.
During the war years he studied soils in Co. Wexford, explored phosphate deposits on the shores of Donegal Bay, worked on the Leinster coalfield, and carried out experiments on the potential yield of fertiliser from potassium-rich rocks, the latter however to null effect. His keeness and hard work led to his promotion (1921) to senior geologist on a wage of £500 a year. After a lull in the activities of the survey during the war of independence and the civil war, he continued his extensive field work. In 1923 his memoir on the occurrence of barytes in Ireland was published, one of his greatest contributions to the geology of Ireland. This report continued to be used as a valuable source of information for mineral exploration in Ireland during the 1950s, ’60s, and ’70s. During 1923–34 he took part in the geological survey in the area of the Liffey river around Pollaphuca, as part of a proposal to construct a hydro-electric generating station. With his director Cole he collaborated on Handbook of the geology of Ireland (1924), which remained the standard text on the geology of Ireland for the next thirty years.
On the death of Cole (1924) he became the senior surviving officer, and for the next four years he took on the duties and responsibilities of acting director but received neither official recognition nor financial reward, despite several letters to the higher authorities. That same year (1924) the geological survey was transferred from the Department of Agriculture and Technical Instruction to the Department of Education, in a move that stymied the activities of the survey for several years. The Department of Education appeared to have little understanding of, or interest in, the activities of the survey. The only publication of note during that era was the first small scale (one million to one) geological map of Ireland published by the survey (1928), which appeared to be devised more for educational use than economic purpose.
In 1928 the survey was transferred again, this time to the Department of Industry and Commerce, and Hallissy's position was at last recognised. He was appointed director (on a salary of £700 a year), a position he retained till his retirement in 1939, aged 70. The survey's activities were once again trained on economic geology and much work was done investigating Irish coalfield resources during those years. Elected MRIA (1911) he was also a fellow (1922) of the Geological Society (London).
A shy and retiring man, he had a reputation for being fair-minded and tactful when dealing with others. He is the only director whose portrait never hung in the GSI gallery. His early operation, which left some disfigurement (he always had a beard), may have made him wary of the artist. He married Pauline O'Donnell from Donegal; they had one son. After a long retirement (from 1939), he died 13 July 1958 at his home, 39 Eaton Square, Terenure, Co. Dublin, aged 88. His wife predeceased him by three months.