William Harper Twelvetrees (1848 – 7 November 1919) was an English geologist who was important for the characterisation of the geology of Tasmania.
[1] He went to Tasmania in 1890 and followed various occupations until August 1899, when he was appointed Tasmanian government geologist and chief inspector of mines.
[2] He was a joint author of a number of articles and books about western Tasmanian geology, including with William Frederick Petterd.
[3][4] In 1914 the office of chief inspector of mines was made a separate one, but Twelvetrees continued to act as government geologist and director of the geological survey of Tasmania until his death.
His writing in the bulletins of the Tasmanian geological survey and other publications, occurred at a very busy time in the West Coast, Tasmania region's mining history, which has not been repeated since.