GLACIAL BEDS. 509 



In parts of West Norfolk, between the Boulder Clay and the Chalk, the line 

 of demarcation is most obscure : it is difficult to say where the one ends and the 

 other begins. In these cases it appears evident that the Glacial Drift was formed 

 chiefly from the Chalk of the district. In this way we may account for some of 

 the very marly varieties of the Boulder Clay, which in places are little else than 

 ground-up Chalk. Analysis of one of these chalky drifts, burnt for lime near Holt, 

 showed 91 per cent, of carbonate of lime, and the Rev. O. Fisher has spoken of 

 this drift as "an ancient manufacture of 'whiting' on a magnificent scale." ^ 

 Mr. Reid observes that "The masses of reconstructed Chalk so common in the 

 Contorted Drift are probably nothing but a later stage of the transported boulders, 

 in this case so shattered and mixed with clay that they form a sort of transition to 

 an ordinary Boulder Clay. From the very marly character of the Contorted Drift 

 when traced westward, it seems not improbable that that portion of the deposit 

 is continuous with, and passes laterally into, the Great Chalky Boulder Clay."^ 

 These remarks furnish a comforting explanation of the difficulties met with in the 

 country around Fakenham. There, where the later Boulder Clay passed directly 

 over the clayey Lower Glacial beds, it no doubt became incorporated with them, 

 causing one contorted mass, and we cannot separate the two deposits.^ (See 

 Fig. 88.) 



In other places we find the flint-layers of the Chalk disturbed, as if that rock 

 had offered a local impediment, perhaps a low hill or cliff against which the icy 

 agent impinged. Mr. Reid has explained the flexures in the Chalk at Triming- 

 ham as due to glacial action in the form of an ice-sheet. Mr. S. V. Wood 

 previously called attention to disturbances in the Chalk at Litcham, and these he 

 attributed to the passage of a glacier over the surface of the rock. Dr. J. E. 

 Taylor drew attention in 1865 to a remarkable 'saddle-shaped ' disturbance in the 

 Chalk at Whitlingham (see Fig. 80, p. 46S) ; * and a pit at Trowse, near 

 Norwich, showed the Chalk uptilted and underlaid by Boulder Drift, so that the 

 disturbance was evidently due to glacial agency. There are also sections near 

 Wells, where the Chalk is similarly disturbed in connection with the Glacial Drift.* 

 These facts help to explain how the huge isolated masses, or "boulders," of the 

 rock may have been formed, and no doubt the Chalk at Trimingham furnishes the 

 most striking evidence of their formation. Mr. Reid remarks : "If the ice-sheet, 

 instead of flowing over the beds, happens to plough into or abut against them, it 

 would bend up a boss of Chalk, as at Beeston. A more extensive disturbance, like 

 that at Trimingham, drives before it a long ridge of the beds, and nips up the Chalk 

 till, like a cloth creased by the sliding of a heavy book, it is folded into an inverted 

 anticlinal. A slight increase of pressure, and the third stage is reached— the top 

 of the anticlinal being entirely sheared off, the Chalk boulder driven up an incline, 

 and forced into the overlying Boulder Clays." ^ While this view seems best to 

 accord with the facts, it is right to mention that Mr. Mellard Reade believes that 

 these boulders were severed from old cliffs by the expansive force of ice in fissures, 

 and then shifted by coast-ice.' (See Fig. 90, also p. 503.) 



In West Norfolk, south-west of Watton, and about li miles north-west of 

 Merton Church, there is a celebrated stone called the Merton Boulder, which 

 measures nearly 12 feet in length, with a thickness and breadth of about four or 

 five feet. The derivation of this rock was long a puzzle to Norfolk geologists, 

 until Mr. Whitaker identified it as Lower Greensand of local origin.* 



The most fertile tracts of the Eastern Counties are situated on Boulder Clay ; to 



1 G. Mag. 1868, p. 551. 



^ See Geology of Fakenham, etc. p. 17. 



^ Geology of the Country around Cromer, pp. 115-117. 



* G. Mag. 1865, p. 324, 1869, p. 508. 



5 P. Geol. Assoc, v. 513; G. Mag. 1881, p. 93; Q. J. xxxv. (Proc), 106; 

 Geol. Fakenham, pp. 9, 24. 



6 Geol. Cromer, p. 115; G. Mag. 1880, p. 61 ; see also O. Fisher, G. Mag. 

 1868, p. 544. 



'' Q.J. xxxviii. 222; A. J. Jukes-Browne, Ann. Nat. Hist. 1880 ; Lyell, Phil. 

 Mag. (3), xvi. 355. 



" Geol. Attleborough, etc., by F. J. Bennett, p. 10. 



