SECOND DAY.] FLIES. 57 



away the larvse and aurelias. May-flies thirty years 

 ago were abundant in the upper part of the Teme 

 river in Herefordshire, where it receives the Clun: 

 they are now rarely seen. Most of the rivers of that 

 part of England, as well as of the west, with the 

 exception of those that rise in the still uncultivated 

 parts of Dartmoor and Exmoor, are rapid and 

 unfordable torrents after rain, and in dry summers 

 little more than scanty rills; and Exmoor and 

 Dartmoor, almost the only considerable remains of 

 those moist, spongy, or peaty soils, which once covered 

 the greatest part of the high lands of England, are 

 becoming cultivated, and their sources will gradually 

 gain the same character as those of our midland and 

 highly improved counties. I cannot give you an idea 

 of the effects of peat mosses and grassy marshes on 

 the water thrown down from the atmosphere, better 

 than by comparing their effects to those of roofs of 

 houses of thatched straw, as contrasted with roofs of 

 slate, on a shower of rain. The slate begins to drop 

 immediately, and sends down what it receives in 

 a rapid torrent, and is dry soon after the shower is 

 over. From the sponge-like roof of thatch, on 

 the contrary, it is long before the water drops ; but it 

 continues dropping and wet for hours after the shower 

 is over and the slate dry.* 



[* The above remark with its illustration is applicable to surface- 



