Biological and physical evidence suggests that the area south-west of Ireland is one of loss from the Celtic Sea. In winter the shelf water there may cascade to 400 m. or even deeper (Cooper & Vaux, 1949). All the evidence suggests that new water enters the Celtic Sea and English Channel over the continental slope between Ushant and the Sole submarine promontory 250 miles to the west. No evidence exists that the Atlantic surface waters are ever rich enough to account for the enrichment of the English Channel observed in the nineteen-twenties. Although the existence then of sufficiently rich oceanic surface water cannot be excluded, it is much more probable that the enrichment was brought about by some form of upwelling. The cause of this is thought to be composite. Only a few times in a century may the component phenomena work together to produce the maximum effect. Each component needs separate study.