The writings of Johannes Walther (1860–1937) have been neglected in the west and his Law of the Correlation (or Succession) of Facies has been ignored or misstated in many textbooks of stratigraphy. Walther should be recognized as a pioneer stratigrapher-sedimentologist, important as both a world traveller and explorer of modern sedimentary environments (deserts, reefs, laterites), and as a theorist. His main theoretical contributions were his championing of the actualistic method for the study of fossils and sedimentary rocks and his founding of the science of comparative lithology. Comparative lithology was seen by Walther as the analogue for sedimentary rocks of comparative anatomy for fossils. It has been neglected in the West until the recent revival of the concept of facies models.
Walther's Law was the key concept within comparative lithology, and was originally stated as follows: “The various deposits of the same facies areas and similarly the sum of the rocks of different facies areas are formed beside each other in space, though in cross-section we see them lying on top of each other. As with biotopes, it is a basic statement of far-reaching significance that only those facies and facies areas can be superimposed primarily which can be observed beside each other at the present time.”
In Russia, Walther's writings appear to have had a greater influence than they have had in Europe and America. They have been partly responsible for the development there of “lithology” as a branch of the geological sciences separate from stratigraphy or petrology.