On the Agricultural Geology of England and Wales. 



481 



Report to the Board of Agriculture, is to the same effect, as to 

 the variety of soils on the chalk, besides the deep white loam of 

 the outcrop of the lower chalk ; and his map represents a stripe 

 of chalk running through the centre of the county, with tracts of 

 clay on the east and west. The eastern tract must be a continua- 

 tion of the till or boulder clay of Norfolk and Suffolk. The 

 western tract consists in part of gault and Oxford clay where they 

 are exposed, and in part of the brown clay of Cambridgeshire, a 

 variety of till west of the chalk ridge. One of the sections given 

 by Mr. Jonas shows a considerable depth of the brown erratic clay 

 on the gault and green sand between Orwell Gap and Gransden. 



Jn Essex, Young's map only allows to' the chalk district a small 

 angle of the county adjoining to Cambridgeshire west of Saffron 

 Walden. " The substratum of the whole county," he says, " is 

 chalk at various depths, which begins to appear within a mile of 

 Walden." About Audley End he describes the hills as chalk, 

 the vales good loam and gravel, but with variations, the soil on 

 the hills not more than five inches deep, and liable to burn in dry 

 weather. His other varieties of soil on the chalk are wet soils ; 

 cold and heavy soils ; soils on a basis of gravel ; good turnip 

 land in the vales and lower slopes, generally dry and good. 



Our geological maps of Hertfordshire assign to the chalk all 

 that area north of a line drawn from Bishop's Stortford through 

 Sawbridgeworth, Ware, Hertford, Hatfield, St. Alban's, Hemel 

 Hempstead, and Watford, with the exception of a tongue of the 

 plastic series extending from St. Alban's as far as Kmgsbourne 

 m the direction of Luton. The chalk, however, Is so covered 

 with the superficial deposits that Young's agricultural map only 

 exhibits as his chalk district, the outcrop of that rock in the N.E. 

 of the county from Royston by Baldock, and in the southern ex- 

 tremity that indentation of green sand which on the geological 

 maps runs in at Hitchin. In this tract, he says, the surface soil 

 consists of two varieties — chalk, without other mixture than that 

 which it has received from ages of cultivation, and marme^ a w^hite 

 marl containing an admixture of clay — both good soils, but the 

 latter the best. A large portion of the chalk of our geological 

 maps is covered by his districts of loam and clay, which, with his 

 chalk district before described, constitute the principal agricul- 

 tural areas into which he divides the county. He observes of 

 them — I should guard the reader against the idea that this is 

 an accurate discrimination. The truth is, that the soils in this 

 county mix and run into one another in such a remarkable man- 

 ner, that, except in the case of the chalk, and that singularly in- 

 fertile land which I term gravel, they are named and traced 

 with a good deal of uncertainty, not for want, I trust, of attention 

 in making the observations, but from the varying qualities of the 



VOL. XII. 2 I 



