The superficial sediments in Start Bay consist of three discrete lithological units, know as barrier, bay and bank deposits. Flint and quartz are the dominant constituents of the barrier deposits with small quantities of rhyolite, felsite and grantie. The bay deposits are mainly fine-grained sediments varying in thickness from about 1 m in the nearshore zone, as a result of winnowing by tidal currents and waves, to a maximum of 28 m in the middle of the Bay. The bank deposits consist of coarse shelly sand, are up to 18 m thick and are located within the general vicinity of the Skerries Bank.
Sedimentological and foraminiferal studies, together with C–14 dates, show that barrier-estuarine-lagoonal environments existed seaward of the modern shoreline in the past and that barriers migrated landward in response to oscillations of sea level during the later stages of the Flandrian transgression.
Available evidence indicates that Start Bay is a closed system under present-day conditions. The influence of the Skerries Bank on wave refraction and energy dissipation along the coast has been assessed. The Hallsands disaster can be attributed to the legacy of dredging shingle from the inter-tidal zone, combined with a critical combination of storm waves, gales and spring tides.