Geology of the Neighbourhood of Weymouth, Sgc. 39 



bury Castle Hill, and spread them over the various broken beds of the oolite 

 formation, along- the under-terrace and line of fault; and have also so com- 

 pletely masked and covered up all the lower beds of the true escarpment 

 below the greensand, that not one of them can be distinctly seen : and 

 although this great escarpment is at least 400 feet above the sea, none of its 

 lower strata are exposed to view, except a bed of clay, which, by casting out 

 a line of springs along its junction with the incumbent greensand, affords a 

 perpetual cause of the land slips which obscure the entire base of this escarp- 

 ment, and prevent our tracing distinctly the great Ridgeway fault at its 

 western termination into the sea*. 



The depth of the dislocations occasioned by this great Ridgeway fault 

 along the escarpment of the chalk appears to vary to the amount of several 

 hundred feet. 



2. Osmington Fault. 



The range of the Osmington fault is east and west, and parallel to the 

 great Ridgeway fault we have just described, at the distance of about one 

 mile and a half to the south : its eastern extremity is lost in the chalk downs 

 near South Holworth, and its western termination is seen in Ham Cliff, three 

 miles north-east of Weymouth. Plate H. fig. 2J exhibits its most eastern 

 section at Upton Hill, in which horizontal chalk beds form the north side of 

 the fault, and subsided chalk, greensand, and Portland stone, the south side : 

 a lime-kiln excavated exactly on the line of fracture, exhibits the disposition 

 here represented. In a section of the hill and water-course, one mile further 

 west, at Osmington Millf, the south side of this fault is formed of subsided 

 chalk and greensand, dipping north ; and the north side formed of chalk, 

 resting on greensand, both inclined slightly to the south. Plate II. fig. 8. 

 shows the western extremity of this fault at Ham Cliff, where the Oxford 

 oolite on its south side has subsided to the level of the Oxford clay on its 

 north side. 



3. Ringstead Bay Fault. 

 Plate II. fig. 11. represents a third and very local small fault, produced 

 apparently by a fracture in the cliflTs, and bringing a subsided mass of Port- 

 land stone and Portland sand into contact with Kimmeridge clay. This 

 fault is more oblique than any part of the two great faults we have been 

 describing; like them it ranges east and west, but can be traced only to a 



• On the north side of Abbotsbury Common, immediately below the Castle, a series of land 

 slips, similar to those on the south side, is indicated by a long range of narrow ponds, supported 

 by the bed of clay, across which the land slips have taken place. t Plate II. fig. 3. 



