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making deductions as to the nature of drift deposits from the land forms in
which they occur.
4. Mechanism of development and stratigraphic age
Apart from facilitating the geomorphological study of the areas in which
patterns occur, it is not yet obvious how air photography is able to facilitate
this part of the study.
Limitations of Air Photography
In spite of the considerable value of air photography, it is important to
stress the following limitations:
1. Much of the routine vertical cover has been flown at the wrong time of the
year. Soil patterns are best observed on cover flown between February and
April; vegetational and crop patterns usually are most easily seen between
March and July. However, for an academic study of this type the cost of
special cover would be prohibitive.
2. The patterns do not always show up on air photographs even when the
subsoil features are present. The technique is thus not entirely reliable for
reconnaisance and plotting.
3. Fine details of micro-relief and of vegetation patterns are normally only
observable using conventional methods of topographical and ecological
survey in the field.
References
Baden-Powell, D. F. W. (1948). The Chalky Boulder Clays of Norfolk and Suffolk. Geol.
Mag. 85, 279-96.
Perrin, R. M. S. (1955). Studies in Pedogenesis: Pt. 2. On Calcareous Till in the Breckland
Ph. D. Thesis. University of Cambridge.
Watt, A. S. (1955). Stone stripes in Breckland, Norfolk. Geol. Mag. 92, 173-4.
West, R. G. (1962) (In the press) Problems of the British Quaternary. Proc. Geol. Assoc.
London 73.
Discussion
Mr. J. L. Retzer (U.S.A.): 1. What are the clay mineral types? 2. Has ice wedging been
considered? Answer: 1. The clay mineral assemblage is probably unimportant, as the soils
concerned are extremely sandy (clay contents as low as 0,5%). 2. Yes, the patterns are certain
ly of periglacial origin. However, the speaker did not wish to equate them with any others
until he had more data.
Mr. R. F. Tomlinson (Canada) noted that similar patterns have been observed in Canada,
most commonly on clay soils. They are, in fact, used as a broad photo-indicator of a clay soil.
Dr. Perrin was fairly certain that disturbances, similar to those he has shown, are present in
many places in soils of heavy texture. It is, however, noteworthy that in these cases they are
not readily observed on aerial photographs.
Several of those present drew attention to conformations similar to the patterns discussed.
Prof. Radforth (Canada) and Dr. Vink (Neth.) mentioned cases where they are found under
what are still periglacial conditions (resp. Ellesmere Island and Greenland) whereas Mr.
Grove (U.S.A.) mentioned Kansas and Oklahoma where they, probably wrongly, have been
described as gilgai.
