Gregory remained at the museum until 1900 and was responsible for a Catalogue of the Fossil Bryozoa in three volumes (1896, 1899 and 1909), and a monograph on the Jurassic Corals of Cutch (1900).

He obtained leave at various times to travel in Europe, the West Indies, North America, and East Africa.

The Great Rift Valley (1896),[2] is an interesting account of a journey to Mount Kenya and Lake Baringo made in 1892–3.

Gregory's polar and glaciological work led to his brief selection and service in 1900-1 as director of the civilian scientific staff of the Discovery Expedition.

Another volume, The Climate of Australasia (1904), was expanded from his presidential address to the geographical section of the Australasian Association for the Advancement of Science which met at Dunedin in January 1904.

This does not give a complete impression of Gregory's activities in Australia, for he was director of the Geological Survey of Victoria from 1901, in which year he was elected a fellow of the Royal Society, London, and he was able also to find time for university extension lecturing.

In 1904, Gregory was awarded the chair in Geology at Glasgow University winning against Thomas James Jehu, Philip Lake and others.

He made several expeditions including one to Cyrenaica in North Africa in 1908, where he showed the same interest in archaeology as in his own subjects; another was to southern Angola in 1912.

The expedition, sponsored by the Royal Geographical Society in London, made the first geological traverse of the central Andes of Peru.

He was in Gregory's canoe and narrowly escaped death when it overturned and later wrote about the expedition in his own autobiography and for the Royal Geographical Society.

Most of his books could be read with interest by both people of science and the general public, and as scientist, teacher, traveller, and man of letters, he had much influence on the knowledge of his time.

Like many other intellectuals and writers during the 1920s, Gregory held Scientific Racist views based on Galtonism and the belief that opposition to cross-breeding in animals could be applied to miscegenation.

In 1931, with Sir Arthur Keith, he delivered the annual Conway Hall lecture entitled Race as a Political Factor.