Australian Dictionary of Biography

Cecil Edgar Tilley (1894-1973), petrologist and mineralogist, was born on 14 May 1894 at Unley, Adelaide, youngest of five children of John Thomas Edward Tilley, a civil engineer from London, and his South Australian-born wife Catherine Jane, née Nicholas. Cecil attended Adelaide High School and the University of Adelaide (B.Sc., 1914). He then followed his teacher W. R. Browne to the University of Sydney (B.Sc., 1916), where he studied chemistry and geology, and became a junior demonstrator in geology and mineralogy. In late 1916 he travelled to England to work in the munitions industry. After the Armistice he returned to Australia. Awarded an 1851 Exhibition scholarship in 1919, he went back to England to study petrology under Alfred Harker at the University of Cambridge (Ph.D., 1922). There he was appointed demonstrator (1923) and lecturer (1929) in petrology, and professor of mineralogy and petrology (1931). At Holy Trinity Church, Kingsway, London, on 21 June 1928 he had married Irene Doris Marshall with Anglican rites.

In his early years at Cambridge, Tilley based his work on a suite of metamorphic rocks from Eyre Peninsula, South Australia. The focus of his research turned specifically to contact metamorphism, and he set about unravelling reactions associated with the steep thermal gradients at the contacts between magmas and chalks and limestones. In the process, he discovered and described a number of new minerals. He also worked on regional metamorphism in the Scottish Highlands, pioneered the mapping of metamorphic zones and introduced the concept of the isogradic surface. From about 1950 he concentrated on igneous rocks, in particular the nature and classification of basalts. After his retirement in 1961, he divided his time between his home base at Cambridge and the Carnegie Institution's geophysical laboratory in Washington, D.C., where he continued his research on basaltic rocks in collaboration with experimental petrologists. During his career he published 122 papers, only 35 of which were written with co-authors.

Tilley was a dominant figure in modern metamorphic and igneous petrology. A fellow (1938) and vice-president (1949-50) of the Royal Society, he was awarded a Royal medal in 1967. He was president of the Mineralogical Society (1948-51 and 1957-60), the International Mineralogical Association (1964-70) and the Geological Society of London (1949-50). Tilley won the Mineralogical Society of America's Roebling medal (1954) and the G.S.L.'s Wollaston medal (1960). He also received honorary doctorates from the Victoria University of Manchester (1956) and the University of Sydney (1964), and honorary fellowships from numerous scientific societies.

A tall, broad-shouldered and solidly built man, Tilley had large hands and penetrating eyes that gave no hint of his shyness and modesty. He possessed acute powers of observation, both in the field and with a microscope. His passion for examining rocks in thin-section, on which he spent much time, was driven by what he called the 'supreme exhilaration of the chase'. He brought to petrology a systematic and rigorous working method—exhaustive collection in the field, painstaking petrographic examination, mineral separation and chemical analysis, and complete command of the literature—which he instilled in his research students.

Tilley had spent a year in Australia in 1938-39. After World War II, he made three other extended visits. Encouraged by him, a succession of young Australians went to Cambridge to undertake postgraduate study and returned to hold academic positions in Australian universities. Through them, Tilley influenced the teaching of geology in his native land. He died on 24 January 1973 in his Cambridge home and was cremated; his wife and their daughter survived him.