Herbert Leland Crosthwait

Colonel Herbert Leland Crosthwait, CIE (1868 – 11 September 1940) was a British military engineer and surveyor known for his work with the Survey of India and contributions to international boundary demarcations between Chile and Argentina.

Early life and education Crosthwait was born in 1868, in The Lodge, Bagenalstown, County Carlow, Ireland. The eldest son of Samuel Crosthwait, a flour mill proprietor at The Lodge Mills, and his wife Sarah Eliza Perry. He had several siblings, including Lucy Eleanor (born 1869), Cecil Henry Edward (1870), Edward Gerard Stewart (1871), William Sylvester (1873), Evelyn Mary (1876), Eileen Elizabeth (1880), Leland George (1881), Arthur Samuel (1883), Ernest Jevon (1886), and Elsie Olive (1887). His family had deep roots in Ireland, with ancestors involved in mercantile activities in Dublin since the 18th century, including roles in the Bank of Ireland and Dublin Chamber of Commerce. He was educated at Rossall School (referred to as "Bossall" in the obituary) and at Trinity College Dublin. and produced a key map that influenced the boundary demarcation.

Disregarding the Chilean agent Bolados and the Argentine agent Arenberg, he placed boundary marker 62 south of Lake O'Higgins/San Martín using a pile of stones and a paper inside a bottle, as he was short on time.

He rose to the rank of lieutenant colonel and was appointed a Companion of the Order of the Indian Empire (CIE) in the 1921 Birthday Honours for his services in the Survey Department. He retired as a colonel.

Personal life His younger brother, Leland George Crosthwait, married Katherine Rosa Man on 3 November 1911 at St Luke's, Chelsea, London, connecting the Crosthwait family to the Man family.

Crosthwait died on 11 September 1940, aged 72.