In 1903, du Toit was appointed as a geologist within the Geological Commission of the Cape of Good Hope, and he began to develop an extensive knowledge of the geology of southern Africa by mapping large portions of the Karoo and its dolerite intrusions, publishing numerous papers on the subject. Subsequently, he mapped the entire Karoo System through the complete stratigraphy from Dwyka tillite to the basalt of the Drakensberg. He worked at a furious rate but was known for his painstaking meticulousness, as reflected in his book "Our Wandering Continents". It still bears reading for its creative and closely argued theses in the light of the geology of the day, and is soberingly consistent with modern principles of plate tectonics.