Adrian Moulle, a French mining engineer, was in South Africa in 1881 to report on the diamond fields of Griqualand West as an agent of the Compagnie Francais de Diamants du Cap. His visit appears to have lasted about two years. After his return to France he compiled a lengthy paper (156 pp) that was published in the Annales des Mines (1885) and also as a monograph entitled Memoire sur la geologie generale et sur les mines de diamants de l'Afrique du Sud (Paris, 1885).
The first part of Moulle's report comprised a general overview of South African geology, with many observations of his own. He acknowledges the help of G.W. Stow*, but seems to have made little use of Stow's information on the Karoo strata and older rocks. For example, he does not mention Stow's evidence of the glacial origin of the Dwyka Formation. The gneiss and granites all over the country, from the Cape Peninsula to the Transvaal Bushveld and Matabeleland, he regarded as the oldest rocks. With regard to the succession of strata in the Cape Supergroup he followed A.G. Bain* and Andrew Wyley*. The amygdaloidal lavas at Pniel (near Barkley West, now part of the Ventersdorp Supergroup) and the Stormberg lavas he both included under "melaphyres" (altered amygdaloidal rocks), regarding them as the earliest and latest lavas in an intermittent succession that commenced in Devonian times. These lavas he distinguished from the "diorites" (i.e., Karoo dolerite).
Moulle spent most of his time on the diamond fields, giving particular attention to the working and value of the mines. He surmised that the serpentinous matrix in which the diamonds occur had come from a depth below the granite, where the diamonds had been formed from hydrocarbons in the serpentine. Gaseous hydrocarbons under high pressure might also have forced the serpentine to the surface he thought, and caused its fragmentation in the process.
While in Kimberley Moulle wrote a report, dated 30 March 1881, on a coal field on the Vaal River (presumably that stretching north from Welkom). It was published, with a similar report by Stow, as Reports upon the great coal field of the Central Vaal valley (London?, 1881?).
Around 1907 Moulle visited South Africa again. He met the geologist A.W. Rogers* in Cape Town and discussed with him the developments in local geological knowledge since his first visit. Rogers (1937) described him as "a charming white-haired Frenchman of great conversational powers".