GEOLOGY 



Prior to the deposit of the main mass of coarse gravels there was 

 spread over the greater part of Norfolk an accumulation known as the 

 Chalky or Upper Boulder Clay, a tough unstratified deposit. Like the 

 Lower Boulder Clay, or Till, it contains much Chalk, in the form of pellets 

 and striated pebbles, and little worn flints, many of which are themselves 

 striated. It contains fewer igneous erratics than the older drift, but more 

 Jurassic and Cretaceous detritus ; masses of Kimeridge shale with fossils, 

 and fossils of Corallian, Oxfordian and Liassic ages, as well as Red Chalk, 

 Carstone and other Cretaceous rocks. Blocks of Carboniferous Limestone 

 are likewise found, and from the formation in general a good series of 

 British rocks and fossils might in time be collected. 



The agent which spread this Chalky Boulder Clay eroded here and 

 there deep channels, along which the present streams have re-excavated 

 courses, or it filled ancient valleys effacing the old scenery, valleys which 

 have now and again been re-excavated. 



Mr. C. Reid, in 1880, showed that the contorted beds were in all 

 probability due to the pressure of the ice-sheet during the greatest 

 intensity of cold, at which time by impinging against old cliffs or 

 escarpments of Chalk great masses of the rock were disrupted and incor- 

 porated in the Contorted Drift. Boulders of Chalk in every stage of 

 manufacture were thus found, none of them having been moved more 

 than a few hundred yards. The disturbed Chalk at Trimingham, where 

 the Chalk is bent into a loop, the apex of which has been squeezed into 

 the Glacial Drift, tells of the near formation of one of the huge boulders. 

 It is indeed by no means certain that this is not a detached mass, not- 

 withstanding that the Chalk is exposed for a certain distance along the 

 foreshore. Again at Trowse, near Norwich, Glacial drift was found 

 beneath the uptilted Chalk, which dipped at an angle of about 35°. ' 



On the borders of Chalk valleys near coverings of Boulder Clay, we 

 constantly find evidence of glaciated Chalk, where the undisturbed Chalk 

 gradually merges up into Chalk with shattered flints and much earthy 

 material. Occasionally remains of mammoth and red deer have been 

 found in the disturbed Chalk, and a glaciated tooth of mammoth has been 

 obtained from the Drift at Witton, near Bacton.' 



Contortions indeed occur beneath the Chalky Boulder Clay whatever 

 may be the formation on which it rests, whether Chalk or Crag or earlier 

 Glacial Drift. Thus in the Chalk and Crag at Whitlingham, a saddle- 

 shaped disturbance was at one time to be seen, and again at Litcham 

 another instance of superficial disturbance was described by S. V. Wood, 

 jun. 



In addition to the large masses of Chalk in the Boulder Clay there 

 are occasional large boulders resembling the Spilsby Sandstone (Neoco- 

 mian) of Lincolnshire. One of these, known as the Merton boulder, 

 lies on the estate of Lord Walsingham. Another remarkable boulder of 

 Kimeridge Clay was observed by Mr. Reid at Fodderstone Gap, between 



' See H. B. Woodward, Quart. Journ. Geol. Soc, vol. xlix. p. 146 (Proc), and Address, 

 Trans. Norfolk Nat. Soc, vol. v. p. 353. 



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