A geologist was a scientist that studied the natural materials which formed a planet.
Professor Kyle, a geologist, was the only survivor after the rest of her expedition was wiped out by the Cybermen's androids in 2526. (TV: Earthshock)
Tanya Webster worked as a geologist with the Oil Exploration Group of the Webster Corporation. (AUDIO: Red Dawn)
Dr Nasreen Chaudhry was a geologist doing deep drilling in Cwmtaff in 2020. This awoke some Silurians that had been hibernating beneath the area for millennia. (TV: The Hungry Earth)