In over-emphasizing stage and structure Davis could not do justice to his own concept about landforms being a function of structure, process and stage. The criticism against him is that the historical approach continued to dominate in British geomorphology for as long as 1960.
According to many process geomorphologists, Davis delayed the development of this subject for more than fifty years. In reality, the rise of process geomorphology and modern structural geomorphology is considered as a deliberate attempt to redress the balance.
Davis’ greatest omission was that he did not study the detailed mechanics and nature of present day processes. Moreover, he neglected the biological processes. His landscapes appear as if they were deserts, without a plant or tree.
This charge leveled against him becomes all the more serious since his work was based on the well-vegetated temperate mid-latitudes. In view of this omission his choice of the adjective for his cycle seems most inappropriate.
The use of the term ‘normal’ regarding the processes was most confusing, because by ‘normal’ he meant only the running water. In the context of past conditions that have occurred in the past, present conditions cannot be said to be normal.
As regards processes, Davis completely neglected the depositional processes and landforms.
The initial assumption of rapid uplift of a land surface is unsatisfactory. However, this criticism was leveled by Penck, one of his early critics. Penck considered landscape evolution to be controlled mainly by the rate of uplift.
The most frequent argument against peneplanation is that the periods of stillstand of landmasses are not of sufficient duration to permit reduction of wide areas to base level.
No one has been able to give good quantitative data on how long a time would be required for a peneplain to develop. Peneplanation can proceed during slow uplift period provided the rate of uplift is slower than the rate of degradation.
It is doubtful whether the youth- maturity- old age sequence and the landforms associated with each stage actually occur. If we observe a landscape in reality with the features of maturity, it is impossible to prove that it is mature because it cannot be proved that it has been derived from a youthful landscape.
There are certain arguments about this. First, some landscapes have features of both maturity and old age. Secondly, certain landscapes do not fit into any of the three categories.
Actually landscapes show an infinite gradation of form, not the three types. Thirdly, it is doubtful whether surfaces flat enough to be called peneplains can ever be created by slope decline, as the erosive capacity of streams is very low in the later stages.
Fourthly, evidence is lacking that the slopes evolve in the Davisian way. There is also no evidence that steeper slopes are younger than gentle slopes. It is undoubtedly true that in matters of slope form and evolution, the cycle concept has proved misleading.
Further more, environmental change during the Pleistocene will obstruct the cycle running its full course. Davis did not give exact figures as regards time required to run its full course.
On the basis of denudation rates, the cycle may complete its full course in hardly less than 106 years, or it could be much more. Pleistocene climatic change is very complicated, but oscillations have a period of at most 10 years.
Davis himself admitted the existence of polycyclic landscapes. But that is not all. In reality, environmental change means periodic change of process, so landforms will be polygenetic instead of polycyclic.
Thus, it is true that the peneplain would never be allowed to form, so the cycles as advocated by Davis would never be completed. It is a truism that nowhere on the earth’s surface is there a peneplain to have been formed as Davis suggested.
The concept of grade, as defined by Davis, has proved wrong. It is difficult to think of graded rivers and graded hill slopes existing together with a long term degrading of the landscape. According to Schumm and Lichty (1965), any statement about grade needs to be accompanied by a statement of definite time-scale.
The cycle of erosion has been simple, no doubt. But at the same time it is deceptive. It has made its supporters prejudiced and narrow-minded. They are not prepared to see the truth. There is no doubt that Davis was a lucid and powerful writer. His easy style and the strength of argument together make the cycle concept seem more convincing than it really is.
Davis never measured form. Impressions of slope form are totally inaccurate and misleading.
Last but not the least; Davis’ work is an example of the deductive approach. He bases his arguments on certain assumptions and infers from the general to particular. This is unscientific. Scientific method is the inductive approach.
Because of this approach Davis made many mistakes. For example, meandering rivers also occur in landscapes that are otherwise youthful. So meandering cannot be associated with only maturity and old age.
The cycle concept continued to be the teaching tool for a long time. It is all the more surprising that the impact of the cycle was so great that it was applied in various other branches of geomorphology.
It is worthwhile to remember that even at a time when Davis was writing, much important work was being done in geomorphology and geology that had nothing to do with the cycle concept.
A few well-known geomorphologists among many who could be quoted are Wegener (1912) on continental drift, Garwood on the glacial protection theory (1910), Kendall (1902) on glacial overflow channel, and Horton (1932) on drainage basin characteristics. Gilbert’s (1914) work on fluvial processes is well known to students of geomorphology.
The popular image of Davis is one of a man with rather entrenched views on just one topic, the erosion cycle.