Yol. 51.] TERTIARY DATE IN DORSET. 559 



thrusts of so late a date, however, have not hitherto been recorded 

 in this country. 



The Bidgeway fault west of this point becomes a simple fracture, 

 bringing Chalk into contact with Pur beck, Portland, and Kimmeridge 

 Clay in succession. After a course of 13 miles it dies away near 

 Portisham as suddenly as it commenced at Chaldon. It is worthy 

 of notice that along this part of the fault the Oolitic rocks dip 

 southwards, even close up to the fault. If, therefore, they shared 

 in the movement which gave the Chalk a high northerly dip, they 

 must before that movement have had an extremely steep southerly 

 dip, which would bring up the Oxford Clay at no great distance 

 northwards. 



(d) The Litton Cheney Fault. 



This comes into existence abreast of the point where the Bidgeway 

 fault dies out, but about 3| miles farther north. Like the Chaldon 

 fold, it commences as an arch in the Chalk and Greensand, with the 

 steeper dip in the northern side. This structure, however, can be 

 detected only at the eastern end, for elsewhere the arch has been 

 denuded away, and the disturbance exists only as a fault throwing 

 Chalk and Greensand in succession against Kimmeridge Clay and 

 Corallian rocks. It is worthy of remark that the arch in the 

 Upper Cretaceous rocks nearly coincides with a syncline in Kim- 

 meridge Clay near Long Bredy, but that westward the post- 

 Cretaceous disturbance crosses the earlier syncline obliquely, the 

 direction of the former being about W. 16° S., that of the latter 

 W. 3° S. 



The fault differs from those previously described in the fact that 

 the Chalk on its northern side dips southward. There is no evidence 

 here of any overthrusting. 



(2) Intra-Cretaceous Disturbances. 



These have been distinguished from the later group by the fact 

 that the Upper Cretaceous beds lie undisturbed upon them. They 

 do not occur, or are indistinguishable, in the Isle of Purbeck, but 

 are conspicuous in the "Weymouth neighbourhood, and have there 

 caused the great unconformity between the Upper and Lower Cre- 

 taceous rocks. 



In travelling westwards we first get a hint of this unconformity in 

 the conglomerate and erosion at the base of the Gault near Lul- 

 worth, but at the Chalk cliff of Whitenose a magnificent section 

 shows Upper Cretaceous rocks dipping 5° north-eastwards, and 

 resting upon the edges of Purbeck, Portland, and Kimmeridge Clay 

 dipping at 20° to 35° northwards. 1 



1 The overlap of the Oolitic rocks by the Upper G-reensand was first noticed 

 in 1830 by Buckland and De la Beche (Trans. Geol. Soc. ser. 2, vol. iv. pt. i. 

 1S35, p. 10). The section at Whitenose was described and figured by the 

 Eev. O. Fisher in 1854 (Trans. Cambridge Phil. Soc. vol. ix. p. 556). 



