Figure 26. Chirp profile near Marysville, MI (see fig. 25 for location): A, areas of coarse material, probably cobbles and boulders, within clay till; B, area of glacial till exposed at the riverbed; C, first multiple reflection of riverbed. Vertical scale is depth in meters (zero depth is 175.5 m IGLD 1985 based on water level, at the time of data acquisition, at the NOAA Dry Dock gage), using a sound velocity of 1,450 m/s in water and 1,650 m/s in sediment. Click on figure for larger image.