In 1856 Clarke carried out geological work in Tasmania on behalf of the government, but refused an offer of a longterm official appointment there, because of his clerical obligations, which had also caused him to refuse a position at the University of Sydney when it was established.
His most important work was in the Sydney Basin, and particularly in the coal measures. He was involved in a long-running argument with Frederick McCoy of Melbourne University about the age of these coal measures, Clarke relying largely on his field work, while McCoy depended essentially on his laboratory examination of the fossils.
Clarke had wide scientific interests, carrying out researches in meteorology and seismology, and maintaining extensive correspondence with colleagues throughout the world. He also acted as a publicist for science, and specially geology, through a vast array of articles in the press. He made the Royal Society of New South Wales an active and effective body, and that society commemorates him through its Clarke Medal and Memorial lecture.
Clarke's maps formed the basis of the first complete geological map of New South Wales published by the NSW Department of Mines in 1880.
Written by David Branagan.