In India he oversaw a mapping program that focussed on coal bearing strata. The team of geologists made major discoveries. Henry Benedict Medlicott coined the term "Gondwana Series" in 1872. Oldham's elder son Richard Dixon Oldham distinguished three types of pressure produced by earthquakes: now known as P (compressional), S (shear), and L (Love)-waves, based on his observations made after the Great Assam Earthquake of 1897. Richard showed in 1906 the arrival patterns of waves and suggested that the core of the earth was liquid. His younger son Henry became a reader in geography at Kings College, Cambridge.