This 1988 book was the first full-length study ever to be published on the subject of sign language as a means of communication among Australian Aborigines. Based on fieldwork conducted over a span of nine years, the volume presents a thorough analysis of the structure of sign languages and their relationship to spoken languages.

Gregory's remarkable career and his scientific work are detailed and critically assessed. Accounts of his heroic 1893 expedition to the Rift Valley (a term he coined) in Kenya (now the Gregory Rift), his first crossing of Spitzbergen, and his resignation as Leader of the first British Antarctic Expedition of 1901, when racing to the Pole under Scott became the priority, draw on unpublished letters. While in Melbourne he published on mining geology and a series of geography textbooks. His 1901 Lake Eyre expedition in Central Australia initiated the phrase 'The Dead Heart of Australia' and controversy over the source of artesian water. In the Chair of Geology in Glasgow from 1904, he built up the largest first-year geology class in the UK, over 400 students. He worked in every field of geology and every continent except Antarctica. He was also involved with the search for a 'homeland' for the Jews in Libya and Angola. He shrewdly realized that Wegener's Continental Drift Theory erroneously supposed that the Pacific Ocean was wider than now before the Atlantic opened. This led to his influential rejection of Continental Drift. He drowned in Peru traversing the Andes having published over 30 books and nearly 400 articles.