Cowles, Henry C. (1911) The causes of vegetational cycles. Annals of the Association of American Geographers, 1 (1): 3-20 [1]
hist-geo-space-sci.net
Nielsen, Jan K. and Helama, Samuli (2012) Christian Theodor Vaupell, a Danish 19th century naturalist and a pioneering developer of the Quaternary geoscience. History of Geo- and Space Sciences, 3: 143-150 [2]