Barth 1857, vol. 1, chapter IX, pp. 196–199. On p. 199, Barth said, about a petroglyph depicting ancient hunters in the Sahara, that it " … bears testimony to a state of life very different from that which we are accustomed to see now in these regions, … "
Barth 1862–1866. Barth, Heinrich (1862–1866). Sammlung und bearbeitung central-afrikanischer vokabularien; Collection of vocabularies of Central-African languages (3 Volumes) (in German and English). Gotha: Justas Perthes. Volume 1, Volume 2, Volume 3.
de Menocal, Peter B. ; Tierney, Jessica E. (2012) "Green Sahara: African humid periods paced by Earth's orbital changes", Nature Education Knowledge3(10): 12. Available at: Nature Education: Knowledge Project
Kirk-Greene 1962, p. 1. Kirk-Greene, A.H.M., ed. (1962). Barth's Travels in Nigeria: Extracts from the Journal of Heinrich Barth's Travels in Nigeria, 1850-1855. London: Oxford University Press. OCLC6083393.
Kirk-Greene 1962, p. 3. Kirk-Greene, A.H.M., ed. (1962). Barth's Travels in Nigeria: Extracts from the Journal of Heinrich Barth's Travels in Nigeria, 1850-1855. London: Oxford University Press. OCLC6083393.
Kirk-Greene 1962, pp. 3–4. Kirk-Greene, A.H.M., ed. (1962). Barth's Travels in Nigeria: Extracts from the Journal of Heinrich Barth's Travels in Nigeria, 1850-1855. London: Oxford University Press. OCLC6083393.
Kirk-Greene 1962, p. 5. Kirk-Greene, A.H.M., ed. (1962). Barth's Travels in Nigeria: Extracts from the Journal of Heinrich Barth's Travels in Nigeria, 1850-1855. London: Oxford University Press. OCLC6083393.
Kirk-Greene 1962, p. 42. Kirk-Greene, A.H.M., ed. (1962). Barth's Travels in Nigeria: Extracts from the Journal of Heinrich Barth's Travels in Nigeria, 1850-1855. London: Oxford University Press. OCLC6083393.