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1 Glacio-Dynamic Variations in Central New York Drumlins: A Morphometric Analysis Mark Francek Professor Roger Blish Undergraduate Student Department of Geography Central M ich igan University Mt. Pleasant, Michigan i"-' li 11-1'. 0 V \. VV ( IA. 0 -,-...;:: 1=\. If " v I 7-, A. /'0 f- [ f- f= w- r7 ABSTRACT Varying rates of till deformation as a function of surface topography and direction of continental ice advance are linked to pattern and form variations in drumlins. Five transects are examined morphometrically. Transects are selected on the basis of their slope and direction of ice advance. A hypothesis based on variable rates of clast lodgement and till deformation accounts for most of drumlins' spatial characteristics. The Cayuga Trough funnelled most of the ice southward and the large amounts of till mobilized contribute to high drumlin densities. The observed increase in drumlin elongation is linked to local ice surging. Away from the trough, drumlin densities and elongation begin to decrease. These trends are attributed to a less vigorous ice flow brought about by increasing surface slopes and radial ice spread. Drumlin pattern and form can thus act as effective indicators to changes in surface slope and direction of ice advance. KE Y WORDS : drumlins, glacial geomorphology, New York, Finger Lakes INTRODUCTION Drumlins are elongated, oval shaped hills composed of glacial drift which are aligned in the direction of predominant flow of continental ice. They are also morphological features that show regular variation as a function of subglacial stresses upon deformable sediment. With research suggestiong that a majority of sole movement is attributed to bed deformation (Boulton, 1982; Alley, 1987; Brand, 1987), it follows that drumlin pattern and form should faithfully reflect fluctuating subglacial stress conditions. The central New York drumlin field presents an ideal opportunity to study the effect of varying subglacial stress levels upon the spatial characteristics (pattern and form) of drumlins. Throughout the field, the southward advancing glacier encountered a wide variety of topographic conditions. Along the central axis of glacier advance, for example, there was little restriction to ice flow. Only 30 kilometers to the east and west, how- 105

2 ever, nearby escarpments did present a barrier to ice flow and the glacier increasingly radiated from the main ice flow direction. This paper attempts to link three hypothetical ice flow conditions to changes in drumlins' spatial characteristics along five 40- to 70-kilometer transects. These transects are located along varying directions of ice advance and have diverse slope conditions. It is hypothesized that varying rates of subglacial till deformation (Boulton 1987), as a function of slope and direction of ice advance, can help explain drumlins' spatial characteristics. PREVIOUS RESEARCH The New York drumlin field has been examined both morphometrically (Fairchild, 1907; Reed, Galvin and Miller, 1962; Miller, 1972; Mills, 1981; Francek, 1988) and stratigraphically (Fairchild, 1907; Savage, 1968; Grieco, 1977). However, the debate continues regarding the factors contributing to drumlin formation. Theories for drumlin genesis include a glacio-fluvial origin in subglacial cavities (Shaw and Sharpe, 1987), dilatancy (Smalley and Unwin, 1968), erosion of pre-existing drift (Kruger and Thomsen, 1984), pore water dissipation (Menzies, 1979), and accretion due to the pressure melting mechanism (Borowiecki and Ericksen, 1985). Menzies (1989) provides a useful review on the varying theories of drumlin origin. Boulton (1987) attempted to synthesize these various approaches by linking drumlin genesis to varying rates of subglacial till deformation. According to this deformation model, the shear strength of the material composing drumlins must reach values as great as the shear stresses imposed by the ice. If this was not the case, till would be deposited as ground moraine rather than drumlins. Erosion dominates near the glacier's source (up-ice) because till shear strength is higher than applied stress (Piotrowski, 1987, Smalley and Piotrowski, 1987). Toward the ice margin, ice thickness decreases and the buoyant influence of meltwater becomes more important; consequently, there is a decrease in overburden pressure. Ambient shear stresses begin deforming till more readily than up-ice. The actual mechanism for drumlin formation involves pre-existing sediment bodies that are more resistant to flow than the surrounding till matrix. Potential cores for drumlin formation would include more slowly moving clasts (Boulton, 1987) and pre-existi ng obstructions. Cores might also be created through pore water dissipation (Menzies, 1987), dilatancy (Piotrowski, 1987), or the accumulation of sediment in ice cavities (Shaw and Sharpe, 1987). Once the core becomes stabilized at the till / ice interface it serves as a nucleus for more till to accumulate due to the pressure melting mechanism (Boulton, 1987). Spatially, the model suggests downice increases in the number of drumlins. Drumlin formation usually ceases at the ice margin because of the continued decl ine in till shear strength. Till becomes essentially cohesion less and is deposited as moraine. In regard to drumlin form, several authors (Crozier, 1975; Borowiecki and Ericksen, 1985; Harry and Trenhaile, 1987) have noted the general down-ice decrease in drumlin elongation and area as the ice margin is approached. This trend is attributed to the decreased velocity within the ice margin environment and the inability of the wasting glacier to mobilize sufficient amounts of till to construct large drumlins. On the other hand, larger, more elongated drumlins, are associated with higher rates of ice movement and till mobilization (Dornkamp and King, 1971). These observations would seem to coincide with Mill's (1981) finding that drumlin elongation declines where flow lines curve away from the main axis of ice flow. SETIING AND GLACIAL HISTORY The New York drumlin field was probably created by Port Huron stage ice (13,000 B.P.) spreading radially from the deepest portion of the Lake Ontario Basin (Salomon 1974) (Fig. 1). Most of the ice was funnelled southward along the low lying Cayuga Trough. The Valley Heads Moraine represents the outer boundary of this advance. The only other 106

3 ONTARIO NOAT" 20, 40 60I0Il KM Figure 1. Directions of glacial advance in central New York. ice lobe found within the study region is the minor Mohawk Valley Lobe which flowed westward. During glacier retreat, a series of proglacial lakes (such as Lakes Warren and Iroquois) were created between the northward retreating ice mass and the higher ground of the Allegheny Plateau to the south. Bedrock consists of Paleozoic limestones, shales, and sandstones (Fenneman 1938). The two features of major geomorphic importance in the region are the Cayuga Trough and the reg ion's cuestaform topography. The Cayuga Trough has low elevations, ranging from 75 meters near Lake Ontario to 120 meters above sea level near Cayuga Lake. The lack of localized relief (less than 30 meters) in the trough is attributed at least in part to glacial and glacio-fluvial erosion. Seismic, stratigraphic, and topographic evidence (Mullins and Hinchley, 1989) reveal: 1) the overdeepening of Cayuga and Seneca Lakes with their respective bedrock floors at 249 meters and 304 meters below sea level; 2) the presence of tunnel valleys north of Cayuga and Seneca Lakes that are also scoured below sea level; and 3) the removal of most surface expression for the Onondaga Escarpment (Fig. 2). South of the Cayuga Trough, the terrain begins to show the influence of the north-facing Onondaga Escarpment which marks the northern boundary of the Allegheny Plateau. Elevations at the escarpment approach 300 meters and loca l relief can exceed 100 meters. The Tug Hill Cuesta has more gentle (approximately 30 meters) local relief. 107

4 G,... Oop.h.f... on T... 5 } ". TrllnhCt 2 MCt4 :- '".:.;,...,... r:.",! Onondep Escerprnent \ NORTH :to WI. " I '.. Drumlin lree lumet g valleys Figure 2. Transect locations and physical features associated with the central New York drumlin field. METHODS Transect Descriptions and Hypotheses Five transects were selected to assess the influence of slope and direction of ice advance upon the spatial characteristics of drumlins (Fig. 2). Transect 3 (within the Cayuga Trough). for example, is located along the axis of ice advance and where surface slope is minimal (See Figs. 2 and 3). It is hypothesized that this transect's drumlins will be significantly more elongated than those found in adjacent transects. Transects 2 and 4 have moderate degrees of ice spread (deviation of approximately 20 degrees) but increases in slope are more severe than Transect 3. The increase in slope 40 to 60 kilometers south of Lake Ontario is due mainly to the Onondaga Escarpment. Transects 1 and 5 represent areas where ice flow deviated by more than 50 degrees from the main direction of ice advance. Increases in surface slope are moderate in comparison to Tran- sects 2 and 4. For all transects, it is hypothesized that the number of drumlins increase down-ice in accordance with Boulton's deformation approach. Available well log data (U.S. Geological Survey, 1990) generally confirms the reliability of transect surface elevations as an indicator of bedrock topography. The major exception to this generalization is along the Cayuga Trough where subglacial tunnel valleys are over 200 meters below sea level (Mullins and Hinchley, 1989). Morphometric Analysis Drumlins were measured from U.S. Geological Survey topographic sheets at the scale of 1 :24,000 with a 10-foot (3.1 m) contour interval. Borowiecki and Ericksen's (1985, p. 421) definition of a drumlin-an oval shaped hill enclosed by at least two contour lines and aligned parallel to assumed ice flow-was used initially to identify drumlins on maps. Aerial photographic interpretation and 108

5 c g250.. >.!!200 w 150 a) Transect 1 Albion b) Transect 2 450'r c.. g250 >.!! 200 w Distance (kml C) 72 Transect Distance (kml c g250.. >.!!200 w 150 N. Wolcott Wolcott Savannah Seneca Falls L c.. g250 >.!!200 w d) Transect Distance (kml c.. g250 > e) Transect 5 Panther lake Distance (kml Distance (kml Figure 3. Elevation profiles of transects with U.S. Geological Survey topographic quadrangle locations. Transect locations noted on Figure 2. then field work conducted during the summers of 1986 and 1987 identified and excluded landforms that can sometimes mimic drumlin form such as kames, beach ridges, and terrace segments. Based on these criteria, 774 drumlins were documented and analyzed in the study area. Among the statistics used to distinguish the spatial characteristics of drumlins along transects: 1. drumlin density-variations in drumlin density were measured by 109

6 superimposing a 4-square kilometer quadrat grid on each topographic quadrangle (approximately 146 square kilometers) bisecting the transect. 2. drumlin streamlining-as measured by drumlin length/width ratio. Higher I/w values indicate greater drumlin streamlining possibly as a function of higher ice velocities. An analysis of variance using SPSSx tatistical procedures tested for signficant differences between means. A Scheffe mulitiple comparison procedure pinpointed where the significant differences occurred for the five selected transects. 3. drumlin height-estimated by adding one half a contour interval above the highest closed contour. Drumlin base elevation was determined by the first contour that enclosed the streamlined form. 4. drumlin symmetry index-computed by dividing the distance to drumlin summit by drumlin length. Classic drumlins typically have a value of 0.33 or less (Fig. 4) ; drumlins with values of 0.50 indicate symmetrical forms, while drumlins with values approaching 1.0 are shaped like roche mountonee (Harry and Trenhaile 1987). 5. drumlin area-expressed by placing a 0.1-square kilometer grid over 10 drumlins randomly selected from quadrangles along each transect. A total area statistic (TA) estimated the area of all drumlins in the transect based on quadrangle samples. RESULTS OF MORPHOMETRIC AND TRANSECT ANALYSES General Trends The most apparent trend in the data is the lack of drumlins (N) along Transects 1 and 5. These transects deviated from the general direction of ice ad vance by over 50 degrees and have an areal density less than 0.4 drumlins per square kilometer (Table 1). Transects 3 and 4 have the greatest number of drumlins (N). have the highest densities (D). and contain the greatest total area (TA) in drumlins. The number of drum- lins (N) in each transect generally increases down-ice consistent with the deformation approach (Boulton, 1987). While drumlin densities (D) usually increase down-ice, drumlin area (A) declines. Drumlin streamlining, as measured by the I/w ratio, shows down-ice increases in streamlining for Transects 3 but decreases for Transect 4. Streamlining trends in the other transects are less clear. Drumlin symmetry indices (S) reveal that the most oval shaped drumlins tend to be found either where the ice was spreading radially (Transect 1 and 5) or where drumlins are located near the Onondaga Escarpment (eg. the Victor (0.45) and Jordan (0.50) quadrangles in Transects 2 and 4 respectively). These trends are visible on Figure 5 which shows idealized drumlin cross sections based on mean length, height, and distance to summit for quadrangles located within each transect. Drumlin height for all transects failed to show any consistent trend. Cayuga Trough Transect (Transect 3) An analysis of variance procedure indicated that significant differences (F = 58.7 (prob.: ) with 4 and 770 degrees of freedom) existed for mean drumlin streamlining. According to the Scheffe multiple comparison procedure (comparison value = 1.63), the Cayuga Trough sample is significantly more streamlined than other drumlins. The total area in drumlins (TA) is also greater than any other transect. Unlike other transects, drumlin streamlining increases down-ice. Drumlin S statistics all have values below 0.3. This indicates that drumlins along Transect 3 approach the classic drumlin form with a steep stoss slope occurring near the front of the drumlin and a tapered, gentle lee side dominating the rest of the drumlin. Furthermore, S statistic values decline downice, with the steep drumlin stoss slope migrating further and further to the front of the drumlin (Fig. 5). Finally, drumlin distribution is unique. Only interfluves within the trough are studded with drumlins; north-south valleys have few or no drumlins (Fig. 2). 110

7 Dome Drumlin Shope 0) 0=0.50 Horizon"l dial,nee to drl.mlllin.lwnmit from ato.. end (DTS) = 500 m. Drumlin Ingth = 1000 m Claooic Drumlin Shope b) " =0.33 DTS = 333 m. Drumlin length = 1000 m. c) 0= 1.0 DTS = 1000 m. Drumlin length : 1000 m Vert:al EI.ggNlbon = 201 o 100 me'\f'r. LJ Figure 4. Computation and representation of drumlin S statistics. Onondaga Escarpment Transects (Transects 2 and 4) Unlike the Cayuga Trough Transect (Transect 3), where drumlin streamlining increases down-i ce along a relatively flat surface slope, both Transects 2 and 4 show a general down-ice decrease in streaml ini ng along steeper surface slopes. For Transect 4, drumlin streamlining (I / w) and drumlin symmetry (S) show a clear tra nsformation from the classic elongated drumlins in the Oswego East quadrangle to Jordan's dome shaped drumlins at the foot of the Onondaga Escarpment (Fig. 5). The greatest contrast between the two transects occurs for up-ice quadrangles such as the Webster and Oswego East quadrangles. The greater streamlining for the Oswego East quadrangle (7.1 vs. 3.1 for Webster) correlates nicely with a flatter surface slope along the first 32 kilometers of Transect 4 (See Fig. 3d). Radial Spread Transects (Transects 1 and 5) In addition to the low values for both density (D) and total area (TA). drumlin streamlining is low to moderate. Drumlin shape is more domal than the classic shapes along the Cayuga Trough (Fig. 5). 111

8 TABLE 1 Morphometric and Spatial Data by Transect Quadrangle n L/W BH H o D S A TA Transect 1 Hamlin Albion Transect 2 Webster Fairport Victor Bristol Transect 3 N. Wolcott Wolcott Savannah Seneca Falls Transect 4 Oswego E. Fulton Lysander Jordan Skaneateles Transect 5 Pulaski Panther L KEY n = number of drumlins L/W = drumlin length to width ratio BH = drumlin base height (m) H drumln height (m) o orientation of drumlins measured west (+.) or east (-) of north D number of drumlins per 4 sq. km quadrat/total area of quadrats containing drumlins S symmetry index-distance to drumlin summit/drumlin length A drumlin area (sq. km) TA = total drumlin area (sq. km) for entire transect 9.1 SLOPE, DIRECTION OF ICE ADVANCE, AND THE SPATIAL CHARACTERISTICS OF DRUMLINS A till deformation model based on the research of Boulton (1987). Menzies (1987). and Piotrowski (1987) helps ex plain for general density patterns observed in the field. Consistent with model predicitions, there are usually lower drumlin densities in the up-ice portion of the field where, hypothetically, till strength was too high for widespread till deformation. Down-ice, till strength decreased allowing variable rates of till deformation with more resistant sediment bodies forming potential sites for drumlin formation. Again, this seems to be 112

9 Up Ice Down Ice Up Ice Transect 2 Webster Down Ice j Up Ice Transect 3 Victor Onondaga Escarpment Bristol NOl1h WolcOII W OI C OI I Savannah Down Ice Seneca Falls ""'" I Transect 4 /2=oswego Easl ==--- Fulton L YSan d e r Jorden Onondaga Escar pment Down Ice =====:::..sk::a::: n::ea::te::le:::s Up Ice Down Ice Transect askl! th erlake - --' Om 100m Ver1 1cle EJaq :: 10. ' Based on mean drumlin length, heigh!. and distance 10 summit Figure 5. Cross sections of idealized drumlins from each transect. borne out by the general down-ice increase in drumlin densities. The applicabil ity of the model, however, needs to be adapted to the diverse ice and surface conditions encountered along each transect. The Cayuga Trough Transect: Drumlin Formation and Ice Streaming The distribution of drumlins along the Cayuga Trough is unique in that drumlins are absent along valleys. Their absence may be explained by lacustrine burial. Another explanation is that drumlins never formed in the first place. This would be consistent with an ice streaming hypothesis that would produce extending flow conditions. According to Mullins and Hinchley (1989), large volumes of pressurized subglacial meltwater were carried by subglacial tunnel valleys within the Cayuga Trough (Fig. 2). Drift entrained within the meltwater would therefore lack the internal cohesian necessary for drumlin nucleation. These conditions contrasted with the better drained interchannel areas. The higher subglacial water pressures provided by tunnel valleys lowered overburden pressure on the interfluves. With lower interchannel stress conditions, large clasts or pre-existing obstructions would not be eroded and could serve as potential cores for drumlin formation. 113

10 High rates of till mobilization along the central axis of ice flow helped drumlin cores to grow in size. This abundant till supply contributed to the transect's high total area (TA) in drumlins (Table 1). The ice streaming hypothesis is further strengthened by variations in drumlin form. Drumlin streamlining, for example, increases down-ice suggesting the role of local ice streaming (Fig. 6). In addition, the steep stoss side of drum"lins migrates further toward the front of the drumlin in a down-ice direction. This suggests that most deposition occurred leeward of the stoss slope; only in this protected locale could drift resist the shear stresses imposed by increasingly mobile ice. Onondaga Escarpment Transects: Drumlin Formation and Ice Retardation The subglacial drainage network that promoted ice streaming along the Cayuga Trough was lacking for Transects 2 and 4. Instead, the Onondaga Escarpment presented a barrier to ice flow and probably promoted compressive ice flow conditions. As the ice approached the Onondaga Escarpment, retardation increased with lower drumlin streamlining values reflecting increasingly sluggish ice. Increased retardation caused larger clasts to deform less readily than its surrounding matrix. The potential for drumlin nucleation therefore increased and this is reflected by down-ice increases in drumlin density. While drumlin density increased down-ice, drumlin area declined. This is again consistent with the Boulton model. Because till strength declines toward the ice margin, its ability to pack in and around obstructions deteriorates. The difference in drumlin characteristics for Transects 2 and 4 should also be addressed. Transect 2 has smaller drumlin areas and lower streamlining values (Table 1). These trends may be explained by the location of these transects relative to the glacier's source re- Figure 6. A large, highly elongated drumlin streamlined by relatively fast moving ice. View is northeast (Savannah quadrangle 20 kilometers north of Seneca Lake). 114

11 gion in the eastern Ontario Basin. The greater up-ice drumlin streamlining for Transect 4 suggests a more vigorous ice movement from this source region, A byproduct of vigorous ice flow was that more till was available to construct larger drumlins. Transect 2, however, was more isolated from the main thrust of ice flow resulting in a lower degree of till mobilization and lower streamlining values. Radial Spread Transects: Isolation from the Main Direction of Ice Advance For Transects 1 and 5, chances for drumlin formation declined because the region was increasingly isolated from the main thrust of ice flow along the Cayuga Trough. Accordingly, there was a failure to mobilize the large amounts of till necessary for possible drumlin formation. Perhaps the fairly low streamlining values for Transect 5 in comparison to Transect 1 can be attributed to ice abuttment against the westward advancing Mohawk Lobe. CONCLUSION This research suggests that the spatial characteristics of drumlins vary in response to surface slope and direction of ice advance. Drumlin densities generally increase down-ice, with the highest drumlin densities appearing along the main southern thrust of ice flow out of the eastern Ontario Basin. Drumlin streamlining is greatest along the relatively flat surface slopes of the Cayuga Trough. The increase in drumlin streamlining is attributed to ice streaming aided by pressurized subglacial meltwater. Streamlining generally declines where surface slopes increase. The Onondaga Escarpment probably acted as an obstruction to ice flow and hindred streamlining. In general, drumlin form seems to respond readily to changing ice conditions while the factors actually creating drumlins are less readily apparent. Drumlin densities, for example, remain comparable both for extending (Transect 3) and compressive (Transect 4) flow conditions. Nonetheless, Boulton's deformation model can explain for drumlin formation in both situations. This morphometric interpretation of drumlin formation should be viewed only as a working hypothesis until detailed stratigraphic and sedimentological analyses of individual drumlins is conducted. Particular attention needs to be devoted to the initiating role of cores (Savage, 1968; Grieco, 1974) in drumlin genesis. Such research, coupled with morphometric analysis, will provide new insights on the glacier that shaped upstate New York. ACKNOWLEDGEMENTS We are grateful to the National Science Foundation (Dissertation Research Grant SES ) for their support of field expenses. Lenore Francek and Jean Salerno provided field assistance. REFERENCES Alley, R. B. Blankenship, D. D., Bentley, C. R., and Rooney, S. T Till Beneath Ice Stream B-Till Deformation : Evidence and Implications. Journal of Geophysical Research, 92 : Borowiecki, B. Z. and Ericksen, R. H Wisconsin Drumlin Field and Its Origin. Zietschrift fur Geomorphologie, 29 : Boulton, G. S Subglacial Processes and the Development of Glacial Bedforms. In : Research in Glacial, Subglacial, and Glaciolacustrine Systems (ed. by R. Davidson-Arnott, W. Wielching, and B. Fahey) Symposium on Geomorphology, Guelph, Ontario pp Boulton, G. S A Theory of Drumlin Formation by Subglacial Sediment Deformation. In : Drumlin Symposium (ed. by J. Menzies and J. Rose) Balkema, Rotterdam, pp Brand, G., Pohjola, V. and Hooke, R Evidence for a Till Layer Beneath Storglaciaren, Sweden, Based on Electrical Resistivity Measurements. Journal of Glaciology, 33: Crozier, M On the Origin of the Peterborough Drumlin Field : Testing the Dilatancy Theory. Canadian Geographer, 19: Dornkamp, J. C. and King, C. A. M Numerical Analysis in Geomorphology Arnold, London. Fairchild, H. L Drumlins of Central Western New York. New York State Museum Bulletin, 111: Fenneman, N., The Physiography of the 115

12 Eastern United States McGraw-Hili, New York. Francek, M The Spatial Characteristics of the New York Drumlin Field. Doctoral Dissertation, University of Wisconsin- Milwaukee, Milwaukee, WI. Grieco, M. R Drumlin Origins as Interpreted from Till Fabrics. Master's Thesis, Syracuse University, Syracuse, NY. Harry, D. G. and Trenhaile, A. S The Morphology of the Arran Drumlin field, Southern Ontario, Canada. In : Drumlin Symposium (ed. by J. Menzies and J. Rose) Balkema, Rotterdam, pp Krall, D. B Late Wisconsinan Ice Recession in East-Central New York. Geological Society of America Bulletin, 88: Kruger, J. and Thomsen, H. H Morphology, Stratigraphy, and Genesis of Small Drumlins in Front of the Glacier Myvdaljokull, South Iceland. Journal of Glaciology, 30 : Menzies, J Towards a General Hypothesis on the Formation of Drumlins. In : Drumlin Symposium (ed. by J. Menzies and J. Rose) Balkema, Rotterdam, pp Menzies, J Drumlins-Products of Controlled or Uncontrolled Glaciodynamic Response? Quaternary Science Reviews, 8: Miller, J. W Variations in New York Drumlins. Annals Association of American Geographers, 62: Mills, H. H An Analysis of Drumlin Form in Northeastern and North-Central United States. Geological Society of America Bulletin Part 1, 91 : Mullins, H. T. and Hinchey, E. J Erosion and Infill of New York Finger Lakes : Implications for Laurentide Ice Sheet Deglaciation. Geology, 17: Piotrowski, J Genesis of the Woodstock Drumlin Field, Southern Ontario, Canada. Boreas, 16: Reed, B., Galvin, C. J. and Miller, J. P Some Aspects of Drumlin Geometry. American Journal of Science, 260: Salomon, N. R Stratigraphy of Glacial Deposits along the Southern Shore of Lake Ontario, New York. Master's Thesis, Syracuse University, Syracuse, NY. Savage, W. Z Application of Plastic Flow Analysis to Drumlin Formation. Master's Thesis, Syracuse University, Syracuse, NY. Shaw, J. and Sharpe, D. R Drumlin Formation by Subglacial Meltwater Erosion. Canadian Journal of Earth Science, 24: Smalley, I. J. and Unwin, D. J The Formation and Shape of Drumlins and their Distribution and Orientation in Drumlin Fields. Journal of Glaciology, 7: Smalley, I. J. and Piotrowski, J. A Critical Strength/ Stress Ratios at the Ice-Bed Interface in the Drumlin Forming Process : from 'Dilatancy' to 'Cross-over.' In : Drumlin Symposium (ed. by J. Menzies and J. Rose) Balkema, Rotterdam, pp Trenhaile, A. S The Morphology of a Drumlin Field. Annals Association of American Geographers, 65: United States Geological Survey, Well Log Data, New York State Albany, NY. 116