According to Mackenzie, the Aurignacian and Solutrean peoples of Britain traded in shells with Cro-Magnons of France. They later intermingled with later arriving Caucasoid racial types, including the proto-Alpines (Furfooz race), who were brachycelphalic (broad-skulled) and a Lappid race, who had minor Eskimo phenotypic traits. Mackenzie also believed that there was a highly depigmentated racial type in small numbers in Britain during the Magdalenian, perhaps who were also blonde, who intermingled with the "dark Iberians" (p. 60). Mackenzie believed that during the Neolithic, the predominant racial type of Britain continued to be Mediterranoid: "The carriers of Neolithic culture were in the main Iberians of Mediterranean racial type" (p. 126) who traded in pearls and ores. Regarding Bronze Age Britain, Mackenzie devoted several chapters supporting his theory that traders and "prospectors" (miners) arrived in Britain c. 2500 BC, originally from the Eastern Mediterranean (pp. 98–101). This theory was initially developed by Harold Peake, who coined the term "Prospector Theory". In the scientific literature of Carleton S. Coon (1939), the theory was revived, and the Mediterraneans who colonised Britain during the late Neolithic or Bronze Age were associated with the Medway megaliths (or long-barrow Megalithic culture). Joseph Deniker earlier called these colonists "Atlanto-Mediterranean".