Penck is noted for criticizing key elements of the Davisian cycle of erosion, concluding that the process of uplift and denudation occur simultaneously, at gradual and continuous rates.
[1] The areas he studied in detail and based his theories on include the Black Forest in Germany, Puna de Atacama in Argentina and Anatolia in modern Turkey.
[3][4] During the 1920s Penck, with Siegfried Passarge, Alfred Hettner and his father, was the foremost figure in a broad German opposition to the "geographical cycle" theory of William Morris Davis.
As he may have told you, I have enjoyed reading parts of his Argentine monograph, an able piece of work, and I have written asking him to specify the difficulties he finds in accepting the cycle theory.
[3] His book, Morphological Analysis of Landforms, was published posthumously in 1924 by his father as was also his paper Die Piedmontflächen des südlichen Schwarzwald (The piedmont-flats of the southern Black Forest).
Geographer Martin Simons claimed in 1962 that Davis misunderstood and mis-translated parts of the paper leaving a distorted view of Penck's ideas among later workers.