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. 19
