Geology of the Neighbourhood of Weymouth, Sgc. 37 



fig. i, the Portland stone forms the south side of the fault ; and greensand, 

 surmounted by chalk, the north side, — both dipping rapidly to the north. 



The theoretical figure (Plate II. No. 12.) is intended to represent by the 

 dotted lines aa. hh. cc, effects that would be produced by denudation extended 

 to different depths along the line of a fault, traversing such strata as occur 

 along this part of the Ridgeway ; thus a denudation descending to aa. would 

 leave chalk and greensand on the north side of the valley so denuded, and 

 Portland stone on the south ; a denudation to bb. would give the same section 

 on the north side of the valley, and Portland sand on the south ; and in this 

 case it would be difficult to distinguish between these two sands, without the 

 aid of organic remains. A denudation to cc. would give again the same beds 

 on the north side, and Kimmeridge clay on the south : examples of all these 

 three theoretical representations are visible in the course of the Ridgeway 

 fault ; e. g. On the high crest which separates the valley of Bineombe from 

 that of Sutton Pointz, the Portland stone touches the chalk; the surfaces of 

 both rocks at the line of fault presenting a uniform appearance, and uniformly 

 level line, like the surface of fig. 12, Plate II. Near the north-western extre- 

 mity of Sutton Valley, a denudation, analogous to that represented by aa. 

 fig. 12. Plate II., shows the Portland stone touching greensand ; a lower 

 point of the same denudation exhibits the Portland sand in contact with the 

 greensand, as represented at bb. in the same figure ; and on the north of 

 Sutton village the Kimmeridge clay also is brought into contact with the 

 greensand, as represented at cc. 



At Upway, on the northern extremity of the general section, and near the 

 summit of the hiil*=, the Portland stone, covered by Purbeck beds, occupies 

 the south side of the fault, and nearly horizontal chalk its north side, the Pur- 

 beck and Portland beds rising at a high angle northwards towards the fault. 

 Prom Upway, for four miles westward, to the final termination of the Port- 

 land stone at Portisham, the Portland stone is continued on the south side, 

 and the chalk on the north side of this fault ; it is exposed by no section, but 

 the junction can be traced on the surface of the fields. 



Near the village of Portisham, precisely at the western termination of the 

 Portland stone,thefaultdeviates to a south-western direction for about a quarter 

 of a mile, traversing the bottom of a deep and narrow dry valley or comb, by 

 which the road from Portisham leads up to Black Down; the east side of this 

 valley is composed of Portland stone, and the west side of chalk, both attaining 

 a considerable elevation above the bottom of the valley. In the village of 



• Plate II. fig. 1. 



