It may seem overly pedantic, but the morphology of Cogden Beach in Dorset (Country Diary, 6 July) is not related to tidal movements. Rather, it is related to longshore drift. The dominant winds from the south-west drive waves that construct a mainly unsorted beach, which is then sorted into large pebbles at the Portland end of Chesil Beach and fine shingle at the Cogden end. This grading is the result of less dominant winds from the south, which, having less power and operating less frequently, can move a lesser load.
The result is a fine gradation of shingle. While this is well shown on Chesil Beach, it is not unique, and readers may well find it interesting to look for their own examples. Try Porthcawl in Wales for a start.
Cliff Willmot
Bewdley, Worcestershire
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