OF THE UPPER CRETACEOUS IN WEST SUFFOLK AND NORFOLK. 589 



§ 5. Faults and the Change of Strike. 



Prof. Judd has called attention to the frequency of cross faults 

 in the district where a change of strike takes place*. Such is the 

 case in the north of Gloucestershire, where the Jurassic escarpment 

 changes its strike from a northerly to a north-easterly direction, 

 and, again, in Rutland, where it resumes a northerly strike. 



The same phenomenon is exhibited in the district we have 

 described, where the Chalk escarpment changes its direction from 

 north-east to north ; but the faults are much less easily detected, be- 

 cause there are no sharp contrasts in the lithological characters of the 

 beds, like those which exist among the Jurassic rocks, and it is only 

 when a definite horizon, like that of the Melbourn Rock, is followed 

 across the country that anything like good evidence is obtained 

 of the existence of such faults. 



At "West Row, near Mildenhall, a small fault is seen in section ; 

 but its throw is small, and as we were not able to trace the out- 

 crop of the Melbourn Rock round Mildenhall, we cannot say 

 whether there are others ; but the change of strike certainly 

 begins here. 



We feel sure that an important fault is hidden beneath the 

 alluvium of the Brandon river, for, as already stated (p. 565), the 

 horizon of the Melbourn Rock, near Lakenheath Station, is at or 

 below the fen-level, whereas on the northern side of the valley, 

 near Hockwold, it is 40 or 50 feet above the alluvium, and the 

 Lower Chalk forms a prominent ridge which extends westward from 

 Hockwold for a distance of about two miles. There must therefore 

 be an east and west fault, with an upthrow on the north side. 



We also think that there are two parallel faults near Feltwell, 

 between which a narrow block is thrown up, so that the outcrops 

 are shifted eastward for a space, but resume their normal position 

 to the north of Feltwell. This inference, however, depends entirely 

 on the correctness of our supposition that the beds exposed in the 

 old lime-kiln south of Feltwell belong to the Chalk-marl. 



Prom Feltwell the outcrops appear to be continuous as far as 

 Whittington, the strike being nearly due north, and- the beds 

 having a slight inclination in the direction of the strike, so that at 

 Whittington the Melbourn Rock is not so far above the level of the 

 fen as it is at Hockwold and Feltwell. On crossing the Stoke 

 river we find the Totternhoe Stone at a somewhat higher level 

 than that of the Melbourn Rock at Whittington, and as the out- 

 crop of the Lower Chalk here runs north-west for some miles, it 

 looks at first sight as if there were a fault bringing up the lower 

 beds on the JST.W. side of the valley ; but it is probable that the real 

 strike is still nearly due north and south, and it will be seen that 

 a line connecting the outcrops of the Melbourn Rock at Whittington 

 and Marham would not deviate much from this direction. There 

 may be a fault with a northerly upthrow, but there is no clear 

 evidence of its existence. 



* " Geology of Eutland," Mem. Greol. Surv. 



Q. J.G.S. No. 171. 2 b 



