Figure 24.3--The last glacial maximum in North America simulated by a geomorphic model. Ice-elevation contour lines are shown at 0.5-km intervals at 18,000 yr BP. Surface flowlines drawn normal to surface contour lines are solid for grounded ice and dashed for floating ice. Ice-sheet margins are heavy solid lines and ice-shelf grounding lines are heavy broken lines. The edge of the Continental Shelf is taken as the 0.5-km bathymetric contour and is shown as a thin line beyond present-day coastlines. The extent of sea water is the dotted area (Hughes 1987).