The Holland Marsh and Alliston lowlands (1) form two large valleys eroded into Pleistocene sediment. These northeast-southwest trending features are part of a regional set of valleys which extend eastward. The valleys are interpreted as tunnel channels formed by subglacial meltwater over 15, 000 years ago. Between the valleys are uplands (2) characterized by streamlined bedforms composed of Newmarket Till. These streamlined bedforms are drumlins (3), landforms of enigmatic origin formed below ice sheets.

Further Reading

Barnett, P.J., 1991: Tunnel valleys: evidence of catastrophic releases of meltwater, central-southern Ontario; in Abstracts with programs, northeastern section, Geological Society of America, Syracuse, N.Y. p. 3.

Brennand, T.A. and Shaw, J. 1994: Tunnel channels and associated landforms, south-central Ontario: their implications for ice-sheet hydrology; Canadian Journal of Earth Science, 31, 505-522.

Shaw, J. 1996: A meltwater model for Laurentide subglacial landscapes: in McCann, S.B. and Ford, D.C. (eds.), Geomorphology Sans Frontieres; Wiley & Sons Ltd., chapter 7, pp. 181-236

Shaw, J. and Gilbert, R. 1990: Evidence for large-scale subglacial meltwater flood events in southern Ontario and northern New York State: Geology, 18, 1169-1172.

Shaw, J., Rains, B., Eyton, R., and Weissling, L. 1996: Laurentide subglacial outburst floods: Landform evidence from digital elevation models; Canadian Journal of Earth Science, 33, 1154-1168.