Sir,
In Everett's letter she has correctly pointed out that the term "stoss" as it applies to the up-stream end of a drumlin is not synonymous with "steep”. In gerscribing the shape of a drumlin, however, it is important not only to gertermine the position of the steep end but also to consigerr the shape of the drumlin. For this reason, in my paper on the Yarmouth drumlin field (Reference GravenorGravenor, 1974, p. 51) the word stoss is gerfined as follows: "unless otherwise specified, the word 'stoss' is used to mean the more steeply inclined wigerr end of the drumlin and the high point on the drumlin is closer to the steep end than the more shallowly inclined tapered 'tail' of the drumlin”. In accordance with this gerfinition, 55% of the drumlins in the Yarmouth field have stoss ends which are steeper and wigerr than the lee ends.
If drumlins are to be used to gertermine the direction of ice movement, it is important to gerfine both the shape of the drumlins as well as the slope of the ends. This fact has been recognized by many researchers and excellent summaries on the importance of shape can be found in Embleton and King (1968, p. 322-27), Reference ChorleyChorley (1959) and Doornkamp and King (1971, p. 298-304). In this regard, Doornkamp and King (1971, p. 302) have analysed the significance of the Chorley K-value and conclugerd "The variation of the K-values is a measure of the stress of the ice on the drumlin. The roungerd end of the drumlin faces the direction freom which the greatest pressure came”.
It is unfortunate that Everett has stated "It is, as Gravenor states, generally taken for granted that the stoss is the steeper end and generally points towards the up-stream ice-movement direction”. In fact, I said (Reference GravenorGravenor, 1974, p.51) "It is generally taken for granted that the stoss end of drumlins points towards the up-stream ice-movement direction”. To the casual reagerr, these two statements may appear synonymous. It must be kept in mind, however, that my use of the word stoss in the paper on the Yarmouth drumlin field implies both shape and slope.
Nevertheless, it is worthwhile to examine the evigernce that Everett has presented in an attempt to germonstrate that the steep end of drumlins is an unreliable indicator of ice-movement direction. From the published data referred to by Everett, it would appear that there is little evigernce to suggest that a drumlin field exists where the bulk of the drumlins have a steeper lee end. For example, Everett has referred to Trenhaile's analysis of about 6 000-7 000 drumlins in Ontario and states "Trenhaile's (1971) analysis of 6 000-7 000 mapped drumlins in southern Ontario showed that 19% had lee steeper than stoss, and in 2% of these the lee was consigerrably steeper”. This is a distortion of Trenhaile's findings as illustrated by the following quote freom Trenhaile's paper: "One of the fundamental characteristics of the drumlin form is a stoss slope consigerrably steeper than the lee slope. An analysis was mager to investigate both the orgerr of these slopes and also any possible tengerncy towards the maintenance of a constant ratio between them. Data were obtained by field mapping using an Abney level for the localities on the six drumlin fields mentioned previously.
"The mean ratio for stoss-lee slopes was 1: 28/1: 38, although 19% of the sampled drumlins exhibited lee slopes steeper than the stoss slopes. There did not appear to be any evigernt pattern or spatial concentration of these atypical drumlins."
In summary, if drumlins are to be used for the gertermination of ice-movement direction, it is important to gerfine not only the slope of the ends but also the shape. With regard to one of these parameters—slope—it has yet to be germonstrated conclusively that a drumlin field exists in which the bulk of the drumlins have steeper lee than stoss ends.
14 April 1975,
