GEOLOGY 



GLACIAL DRIFT 



The succeeding strata of Lower Boulder Clay, comprising beds of stiff 

 unstratified Till with intermediate laminated muds, tell of Glacial con- 

 ditions when ice extended over the area and temporarily retreated during 

 the intervals when the glacier mud was spread over a limited area. The 

 Till itself contains much Chalk and many glaciated erratic stones. The 

 softer chalky material is often crushed, the deposit having a streaky 

 fluxion-structure, regarded by Mr. Reid as due to the sliding pressure of 

 an ice-sheet. Blocks from Scandinavia, such as the ' Rhomben porphyr,' 

 have been identified. 



The Lower Boulder Clay is best seen in the cliffs at Happisburgh, 

 Bacton and Mundesley. It is overlaid by a mass of contorted loams and 

 sands, the disturbances in which form one of the remarkable features in 

 the ' mud cliffs ' of Cromer. Fragments of Tellina balthica, Cardium 

 edule, Cyprina islandica and Mya arenaria occur in the loams, and more 

 abundantly in the sands. Between Overstrand and Sheringham the beds 

 contain huge incorporated strips or boulders of Chalk — one mass measur- 

 ing 500 feet in length.' In this remarkable instance, as in some other 

 cases, the flint-layers in the Chalk masses were comparatively undisturbed. 

 Elsewhere the masses of Chalk have been crushed, the flints fractured, and 

 the fragments scattered. Again, in other instances the Chalk has been 

 ground up and intermixed with clay, and it forms huge masses of marl 

 which are dug for lime-burning, the lime being well suited for agri- 

 cultural purposes. Many old pits also occur in the fields, whence the 

 marl was formerly dug to put on the land. 



As we pass from east to west, so the Contorted Drift (as it is called) 

 becomes less loamy and more and more marly. In East Norfolk the 

 calcareous loam of Happisburgh and Bacton, which yields a rich soil, 

 constitutes some of the best agricultural land in Norfolk. It extends 

 inland to Ludham, Tunstead, Plumstead and Hamlington. Near Nor- 

 wich, where it is known as the Norwich brickearth, it has been largely 

 worked for brick-making on the borders of Mousehold. In older times 

 it was dug near Markshall, where traces have been found of a Roman 

 kiln situated not far from Caistor Camp. 



Large boulders of basalt, quartzite and other rocks have been 

 occasionally encountered in agricultural operations on the loamy subsoil 

 of the Contorted Drift, and the blocks have been removed to adjacent 

 villages and homesteads, where they are placed alongside buildings for 

 protection or for use as horse-blocks. 



On the coast where the cliffs of Contorted Drift contain great masses 

 of sand, the winds, and especially the easterly and north-easterly breezes, 

 blow away the sand and accelerate the destruction of the cliffs. Adjoin- 

 ing the coast near Cromer and Runton, as Mr. Reid has remarked, 

 occasionally the whole of the top soil of a field may be blown away, 



' See Lyell, ' On the Boulder Formation, or Drift and associated Freshwater Deposits 

 composing the Mud-clifis of Eastern Norfolk,' Phil. Mag., ser. 3, vol. xvi., 1840, p. 345. 



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