Page:Popular Science Monthly Volume 17.djvu/519

Rh, Lewes, Reading, Wallingford, Cambridge, and Beverley, were all places of great mediæval importance, and all stand within the cretaceous area. Other wool-growing tracts of course possessed a similar value.

A few more special agricultural features of the various secondary or tertiary geological formations may here he fitly introduced. The Trias and other "Poikilitic" strata, running across England from the Tyne to the Exe, form beautiful undulating country, comprising much of the best wheat-growing and pasture land, and famous for the production of cheese. In this belt lie the vale of York, the Trent and Severn Valleys, the Cheshire Plain, and the vales of Exeter and Taunton. An outlier forms the valley of the Eden at Carlisle. The Lias, which follows the Poikilitic series to the southeast, is a good soil for corn and apples, but also produces the most excellent cheese in England, as Mr. Woodward has pointed out. Along the Severn bank it furnishes the double Gloucester; at Melton Mowbray and Leicester it produces Stilton; and in Somersetshire it unites with the triassic red marl to yield the Cheddar. The fruitful vales of Eversham and Gloucester belong to this formation. The Oölite gives us the rock known as cornbrash, which disintegrates into a splendid wheat-bearing soil, naturally manured by its large quantities of phosphate of lime, the so-called bone-earth. The Oxford Clay, on the other hand, is poor and hard to cultivate, so that most of it lies under permanent pasture. It forms the sheep-feeding vale of Blackmore, in Dorset. The Kimmeridge Clay, in like manner, does not repay cultivation, and is mostly employed for meadow or woodland. The Wealden, forming the great trough between the North and South Downs, is another of the infertile soils. It remained a great wood, the Andredesweald, or Forest of Anderida, for a long period after the English conquest, and the local names of the district still retain their forestine terminations of hurst, ley, den, or field. Even at the present day the Weald is damp and clayey land, little tilled, and either laid down in pasture or given over to furze and heath. The Gault makes good grazing-lands, and the Upper Greensand is in every respect a fertile formation. These two series yield the rich Vale of White Horse, through which the Great Western Railway runs between Swindon and Didcot, as well as the vale of Aylesbury, whose name has become synonymous with pure milk. The Chalk supplies us with South Down mutton, said to owe its excellence not so much to the pasture itself as to a small land-snail (Helix virgata) which the sheep devour in great numbers. The London clay, though stiff, can be made to yield good crops. Drift forms