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materials, nor under “rock”, which implies hard materials. In his answer, Prof. Miles made 
it clear that the term “drift” is a broad parent material type. It is used essentially as un 
differentiated material except with respect to origin. He considers that different drift types 
also weather in place to produce the engineering soil profile. The tables indicated in the paper 
are not closed tables. In an area where decomposed rock exists to great depths one could add 
another column to Table 6 to cover the residuals. After seeing the complex agricultural 
soils of the Netherlands the speaker believes we also need a column for man-made drift. 
Dr. A. P. A. Vink (Netherlands) had the following questions: 1. What, in Prof. Miles’ con 
cept are “small” map scales and “large” map scales? 2. What is the minimum depth of 
loose material for a profile to be called “soil”? 3. What is the concept of “engineering soil 
group”? Is it 2- or 3-dimensional? 4. What is the definition of “horizon” in Prof. MrT.Es’ 
concept? Prof. Miles gave the following answers: 1. A large scale map is 1 : 1,200 to 1 : 6,000. 
A small scale map is 1 : 20,000 to 1 : 62,500 or smaller. 2. The answer to this should be 
that a one inch layer or less of unconsolidated material on rock would form an engineering 
soil profile. In practice, we usually waste or remove in clearing operations about 6 to 12 inches 
of the profile. 3. Definitely a three dimensional body. The unified engineering soil classifica 
tion system (Casagrande) is definitely applied by American engineers throughout the world. 
I do agree that we should prefix the group symbols with “I” to show that it is inferred or 
identified by the technique of airphoto interpretation. 4. A horizon is any layer that has 
engineering properties. Usually the profile and component horizons are generalized as A, B, 
C, and D, where C is the parent material of altered rock or drift as outlined in the paper. 
The D layer is the dissimilar drift or sound rock underlying the unconsolidated material.