Go to the Main Scottish Cave and Mine Database Search Page

Letterbox

N of St Abb's Head, Berwickshire.

A dive only subtidal cave/tunnel in a reef called 'West in Thirle Rocks'.

BN03CV03, Letterbox, is a tunnel through a rocky reef in West in Thirle Bay, mid-way between Petticowick Bay and Thrummie Carr. The reef lies approximately 30m from the nearest shore to the south and approximately 400m due west of the slipway in Petticowick Bay (this information updates the details mis-reported for this site in ERT, 2000). The un-named [West in Thirle Rocks OS!] rocky reef is just covered during spring high water. The larger western entrance is on the shore-side of the reef, approximately 10 to 20m west of its highest point. The tunnel is 4.5m wide by 3.3m high at the entrance overall, although there is a large boulder jammed into the entrance which reduces the effective width to 2.5m. The tunnel was measured at 15m long and has an approximately west-southwest to east-northeast orientation.

Both the entrance and exit are in the lower infralittoral at 7 to 8m BCD. The tunnel is generally 2m wide at floor level, though its triangular cross section restricts the effective swimming width to about 1m. At about 10m into the tunnel, a boulder on side 1 causes the effective width to be reduced to just under 1m. The ceiling is low throughout (just over 1m high at its lowest point) and mid-way through the tunnel there is a slit-like opening to the infralittoral environment outside high up on side 2. The tunnel floor consists of scoured cobbles for the most part, with one small patch of mixed sediment in the narrowest section near the exit. [SNH Report 069]

Alternative Names: Letterbox Tunnel, Letter Box Tunnel

Notes: Access: dive only.

NGR adapted from Report 069 which gives the NGR of their shotline as NT 90427 69119 which is about 5 m west of the underwater west entrance.