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Sir Jethro Justinian Harris Teall (5 January 1849 – 2 July 1924) was a British geologist.
He was born to Jethro Teall (1816-1848) and Mary Hathaway (1820-1880) in Northleach, Gloucestershire. He studied at St John's College, Cambridge. In 1874, he was awarded the Sedgwick Prize for his study of lower-level greensand, a form of sandstone. He was elected a Fellow of the Royal Society in 1890, mainly on account of his book British Petrography, written in 1888. He won the Wollaston Medal of the Geological Society in 1905. Teallite is named for him. He was awarded D.Sc. degrees by the University of Dublin and the University of Oxford and an LL.D. by the University of St Andrews. In 1901, he became the director of His Majesty's Geological Survey, personally completing much work in north west Scotland. He was knighted in 1916 for his contribution to the survey.
He married Harriet Moore Cowen (1856-1940) in 1879 and had two children, Major George (1880-1939) and Frederick Teall (1882-1952). He was a member of the Athenaeum Club, London. He died in Rosendale Road, London, in 1924.