First Sentence

"Fourteen miles to the south-west of Plymouth astride the approach to its great harbour, the fairway of the English Channel is broken by a triple reef. The rust-red rocks of which it is composed are a rare form of granitoid gneiss found in only one other area of the British Isles, at Prawle Point twenty-seven miles away: an indication that in the remote pre-Cambrian past the reef was joined to the mainland."