GEOLOGY 



ESSEX occupies a large part of the irregular tract which is known 

 to geologists as the London Basin, and which has for its frame- 

 work the great Chalk formation. The southern rim of this 

 Basin rises in the North Downs of Kent, whence the Chalk 

 slopes gradually to the borders of the Thames at Erith and Gravesend, 

 comes to the surface in south Essex at Purfleet and Grays, and then sinks 

 below ground over the greater part of the county. The northern rim of 

 the Basin appears in the downs of Dunstable, Luton and Royston, and 

 in the uplands of Heydon and Saffron Walden in Essex. 



The contour of the Chalk Basin is to some extent modified by slight 

 undulations and fractures along the Kentish side of the Thames between 

 Greenwich and Erith, so that while the curvature is for the most part 

 gentle, the inclination becomes somewhat steeper on the southern side of 

 Essex. Hence at Dagenham, Rettenden and Southend the Chalk is 

 about 400 feet below ground, at Chelmsford it is about 360 feet, and 

 thence northward it more gradually approaches the surface. Near Hey- 

 don however there are some striking evidences of local disturbance, to 

 which further reference will be made. 



Resting in the hollow of the Basin, and conforming generally with 

 its curvature, is a series of Eocene strata, the most important of which is 

 the London Clay. The succeeding deposits include small outlying tracts 

 of Crag, but they consist chiefly of the irregular and variable accumu- 

 lations grouped as ' drift.' These lie scattered over the uplands in the 

 form of gravel and Boulder Clay, and are spread along the river valleys in 

 the form of gravel, brickearth and alluvium. 



The structure of the ground is thus comparatively simple, but there 

 are difficulties in the determination of the relative ages of some of the 

 scattered superficial deposits. There are grave difficulties also when 

 it is sought to decipher the underground rocky structure beneath the 

 Chalk and other Cretaceous strata. The problem is of the highest 

 interest and practical importance, but it raises questions which deep 

 borings alone can solve. 



Although the county is essentially a flat one, and especially along 

 the river and sea coasts which are bordered by marshes, yet inland there 

 is an abundant variety of soil, and these regions are very pleasantly diver- 

 sified with arable land and pasture, with woodlands, commons and well- 

 timbered hedgerows. Indeed to quote an old agricultural work, ' Every 

 species of soil, from the most stubborn to the mildest loam, is to be 

 found.' 1 



1 General firm of A 'grit. ofEtiex, by Messrs. Griggs, 410 (Lond. 1794), p. 7. 

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