CLIMATIC INFLUENCES 253
like Abridge. The influence of London on sunshine amounts and fog fre-
quency has already been indicated. The formation of an inversion layer over
the industrialised areas of the Lea valley is facilitated by the presence of a
thousand acres of deep reservoir water and nearly 20 square miles of marsh-
land. The valley is an obvious fog funnel north from London. The haze
hood over London peters out over Epping Forest, but over the industrialised
south-west of the district its protection against loss of temperature is
discernible in temperature traverses (Fig. 2). These also show that the