154 INSECT PESTS 



deposit. In fact, Lyell, the famous geologist, called 

 this and the associated strata Eocene, which simply 

 means "recent." Of itself London Clay is barren and 

 unkindly as a growing medium, but as there are numerous 

 caps of sand and gravel, and it has been highly cultivated 

 in times past by a numerous population, it generally 

 yields good results. The London Clay and Eocene 

 deposits cover another broad triangle, north of the Downs 

 this area embracing the Thames Estuary as far as Whit- 

 stable on the south side, and extending northwards along 

 the coast to Yarmouth, the inland Hmit or apex of the 

 triangle being at Basingstoke, A second area, a strip 

 about twenty miles wide, exists to the south of the Downs, 

 and extends along the South Coast from Selsey to Pur- 

 beck, and passing under Southampton Water, reappears 

 in the northern half of the Isle of Wight. 



Clay itself is made up of the decomposed particles of 

 various older rocks, trap, basalt, greenstone, etc., which 

 have been carried down and deposited at the mouths 

 of former rivers in bygone ages and pressed together 

 by their own weight, often embedding shells, flints, 

 pebbles and plants indiscriminately into a solid mass. 

 China clay, almost peculiar to Cornwall, is merely decom- 

 posed gram'te. 



We have now seen in brief how the soil in England is 

 founded on various geological deposits, and these are 

 bound to affect the nature of the soil in each particular 

 place, but we must not suppose that the rock bottom 

 absolutely decides the composition of a soil, for many 

 other agencies have been at work in the past, and are 

 indeed always in operation even now. Let us study for 

 a moment the two sections shown. No. 1 gives us the 

 strata mentioned in the foregoing description of the rocks 

 of England as they were originally deposited. If this 

 condition of things had obtained we should have known 

 little or nothing of the crust of the earth beneath us, but 

 seeing that elevations, depressions, crumplings and out- 



