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Rivers are essential for loess deposit formation. River systems which relate directly to loess deposit formation include the Danube and the Rhine; the Mississippi and the Missouri; the Thames and the Medway; the Indus, Ganges and Brahmaputra; the Dnepr, Don and Volga; the Clutha, Mataura and Rakaia-New Zealand rivers; the Yellow River; rivers in South America; Siberian rivers (flowing north); the Odra and the Wisla (between the mountains and the ice); the Syr-Darya and Amu-Darya (into the desert).

The contention is that rivers are not just important in major loess deposit formation, they are mandatory (necessary, imperative, obligatory, essential, indispensable, requisite). For a complete and satisfactory study of a loess deposit, we need to know how the material is produced; how it is transported and distributed across the landscape; how intermediate deposits are formed; how transportation provides the defining properties (i.e., open structure, collapsibility, draping across the landscape); and what may happen post-deposition (e.g., chernozemisation, fragipan formation, increased collapsibility, etc.).

If rivers are essential then it would appear that the British loess is probably Alpine material delivered by the proto-Rhine and the Polish loess is not derived from the ice-sheet to the north but from the mountains to the south. The lack of loess in Canada is explained by the absence of suitable rivers. The loess in Russia and neighbouring countries can be classified (as Jefferson et al. [Jefferson, I.F., Evstatiev, D., Karastenev, D., Mavlyanova, N.G., Smalley, I.J., 2003b. The engineering geology of loess and loess-like deposits: a commentary on the Russian literature. Engineering Geology 68, 333-351] suggested) on the basis of associated rivers. A ’new’ deposit of glacial loess is recognised-associated with the Dnepr, Don and Volga rivers (the USWR loess). The Smalley-Leach [Smalley, I.J., Leach, J.A., 1978. The origin and distribution of the loess in the Danube basin and associated regions of East-Central Europe: a review. Sedimentary Geology 21, 1-26. Available from: < www.geo.edu.ro/sgr/mod/downloads/PDF/Smalley-SedGeo-1978.pdf >] vision of the loess in the Danube basin and East-Central Europe is probably misconceived. They assigned a great significance to glacial action and put loess in a ’northern band’. It appears that this proposed glacial influence is minimal and that the Danube loess is essentially mountain loess-derived from the Alps, the Carpathians, the Sudeten mountains and other high regions. The Danube system is a classic example of a river controlling loess distribution. (C) 2008 Elsevier Ltd and INQUA. All rights reserved.