486 On the Agricultural Geology of England and Wales. 



spread, more or less, over the whole district. The greater por- 

 tion of the New Forest, marked as London clay, is a continuation 

 of the freshwater or rather estuary strata of the Isle of Wight^ 

 which reappear in Hordwell Cliff. The attenuated representatives 

 of the London and plastic clay — the former under the form of a 

 ferruginous sandy loam — occupy a very narrow band bordering 

 the chalk. The remainder of the space, coloured on existing 

 geological maps as London and plastic clay, consists of sands and 

 clays, which are the equivalents of the upper, middle, and lower 

 Bagshot beds, of the London tertiary district, established by Mr. 

 Prestwich. To the lower Bagshots belong the sands and white 

 clays of Poole and Corfe Castle ; to the middle Bagshots, the 

 clays of Barton, and the sandy clays and clayey sands of Christ- 

 church Head; to the upper Bagshots, the glass-house sand of 

 Headon Hill, in the Isle of Wight, which is there immediately 

 below the freshwater clays and marls, and which reappears 

 beneath those strata and above the Barton clay in Hordwell 

 Cliff. 



But to return to the chalk. It remains to trace the variations 

 of soil upon it, through Dorsetshire and on the North and South 

 Downs, as laid down by agricultural authorities. The ' Report 

 on Dorsetshire,' to the Board of Agriculture, is by Stevenson. 

 He tells us that the soil of the more elevated parts of the chalk 

 district is a thin loam, incumbent on rubbly chalk, below which 

 is compact chalk ; and that in those cases in which the soil is 

 only two or three inches deep, the land cannot be ploughed to 

 advantage, as the mixture of the loose chalk is pernicious. He 

 adds, that the poorest parts of the Downs are the steep acclivities 

 which overlook the vale of Blackmore, and the most fertile 

 those which border the sandy district (eocene tertiaries) between 

 Wimborne and Dorchester. In some places flints are numerous. 

 Between Evershot and Cerne he describes deep beds of gravel, 

 flints, and clay, as covering the chalk. Wherever the strata in- 

 cumbent on the chalk consist of deep sand and gravel, the sur- 

 face is generally covered with furze or heath, the latter seldom 

 appearing where the chalk is at no great depth. The vales are 

 in general covered with deep gravel, loam, or clay^ " which may 

 be supposed to have been washed from the contiguous hills in 

 the general inundation. Some people," he adds, seem to enter- 

 iain the opinion that the natural soil, or vegetable mould, is 

 originally of the same nature as the substratum, below the usual 

 depth of ploughing ; but the appearance of the chalky districts 

 would induce a belief that the cultivated soil was the last sedi- 

 ment of the water which formerly covered the earth." He in- 

 fers, from the appearance of the Celtic and Roman earthworks— 

 which are, in many instances^ as bare of vegetation as if they had 



