Figure 14. Map showing the surficial geology of Vineyard and western Nantucket Sounds with equivalent onshore geology (adapted from Stone and DiGiacomo-Cohen, 2009). The areal extents over which offshore subsurface geologic units crop out at the sea floor were interpreted from seismic-reflection data. See figure 9 for detailed descriptions of the offshore geologic units. Holocene sediment veneers too thin to be detected in the seismic data (less than approximately 0.5 m) may overlie outcrops of older units locally. The bathymetric hillshade relief map is derived from the composite bathymetry in figure 3. Black lines indicate chirp profile locations (figs. 10, 11, and 12) and red lines indicate geologic section locations (fig. 13). Qdm, Pleistocene glacial moraine – Martha's Vineyard and Buzzards Bay moraines; Qdt, undifferentiated Pleistocene glacial till and ice contact; Qdl, Pleistocene glaciolacustrine (glaciodeltaic and lake floor) Qdf, Pleistocene glaciofluvial (outwash); Qfe, Holocene fluvial and estuarine; Qmn and Qmd, Holocene nearshore and deepwater marine. The locations of Lucas (L), Middle Ground (MG), L’Hommedieu (LH), Hedge Fence (HF), and Squash Meadow (SM) Shoals are also indicated.