Ganly, Patrick (1809–99), geologist, was born in Dublin. His family came from the Longford-Roscommon area, where his father Patrick may have worked for William Edgeworth and Richard Griffith (qv) during their survey of Co. Roscommon (1814). At the age of 18 young Patrick joined Griffith's staff in the boundary survey (1827) and then the ordnance survey (1830–33). He moved to the valuation department in 1833, where he worked under Griffith as virtually a full-time field geologist. In his obsessive drive to produce the first geological map of Ireland, Griffith ran what could be said to be an entirely unauthorised geological survey of Ireland from within the valuation office. Ganly's 600 letters (1837–46) to Griffith and his assistant John Kelly, rediscovered in 1944 and now in the RIA, record his extensive and detailed geological field observations from all around the country, and show his enormous contribution to the accuracy of Griffith's quarter-inch map, first produced in 1839. The map was exhibited at the Great Industrial Exhibition held in Dublin in 1853, and the following year Griffith received the Wollaston medal, with admiration for ‘one of the most remarkable maps ever produced by a single individual’ (Geikie, 1905). Griffith made few references to Ganly's services, either to hide the misappropriation of funds, as Ganly was supposed to be a draughtsman in the valuation office, or because he did not want to share credit with anyone. From the tone of the letters, the relationship between the two men often appears forthright, with little subservience from Ganly. In 1841 he enrolled as an external student in TCD, and spent the winter evenings studying sciences and languages, receiving his BA in 1849, coincidentally at the same ceremony at which Griffith received an honorary LLD. On the completion of the general valuation of Ireland (1851) he was given his notice. He proposed to emigrate to the USA, but in 1853 Griffith found further employment for him in the valuation office. A second map brought out in 1855, with extensive revisions by Ganly, remains to this day the most accurate representation of the geology of some parts of Ireland.
An astute and perceptive field geologist, Ganly gained posthumously an international reputation from his discovery of the use of current-bedding to determine the orientation of strata, first published in 1856 (Journal of the Geological Society of Dublin, vii, 164). However, his contemporaries did not appreciate his findings and they went largely unnoticed. Cross-stratification as evidence of orientation of bedding was rediscovered in the 1920s by American geologists and has been in everyday use by geologists ever since.
After his retirement (1860) he appears to have practised as a civil engineer. He is known to have married Mary Elizabeth and lived at 29 Bath Avenue, Sandymount, Dublin, from 1872 to 1894. They had one son, who died aged 20 in 1874. Ganly died 29 October 1899 at 52 Donnybrook main street, Dublin; he is buried in an unmarked grave in Glasnevin cemetery. To honour his enormous contribution to Irish geology, the exhibition hall in the Geological Survey of Ireland building at Beggar's Bush, Dublin, is named the Ganly Gallery.