Figure 11. Boomer sub-bottom profile that crosses over the railway tunnels in the northernmost St. Clair River area with seismic stratigraphic interpretation. Vertical scale is depth in meters (zero depth is 175.9 m IGLD 1985 based on water level, at the time of data acquisition, at the NOAA gage at the mouth of the Black River), using a sound velocity of 1,450 m/s in water and 1,650 m/s in sediment. (See table 1 for explanation of stratigraphic units and unconformities; see fig. 10 for profile location.)