James Merriman Archer Thomson (1863-1913) was a British rock-climber and mountaineer. He climbed extensively in North Wales with others such as Oscar Eckenstein. He was a believer in leading on sight, and was not keen on O. G. Jones's practice of surveying a route with a top-rope. He extensively explored the cliffs of Y Lliwedd, and with A. W. Andrews produced the first official climbing guide to the cliff (published by the then-recently-founded Climbers' Club) in 1909; he authored the second, to the Ogwen District, the following year). From 1896 until his death (by suicide?) in 1913 he was Headmaster of Llandudno County School.
