Geology of the Neighbourhood of Weymouth, 8^c. 35 



the lines of elevation ; and accordingly our district affords examples of troughs 

 and depressions thus produced in the case of the Purbeck beds lying- upon a 

 trough of Portland stone at Upway, and of Kimmeridge clay in a trough of 

 Oxford oolite at Abbotsbury*. 



HI. Contortion. 



At Upway in the quarries west of the Church, we have examples of con- 

 tortion produced by the elevation of the strata, similar to those represented 

 by Mr. Webster in his drawings of Lulworth Cove and the coves adjacent to 

 it, in the Isle of Purbeck. Throughout the whole Weymouth district, and 

 particularly along the lines of fault, which we shall next describe, contortions 

 of greater or less amount are too numerous to require individual speci- 

 fication. 



IV. Faults. 



In a district which has been so much dislocated, the elevations and depres- 

 sions just described lead us to expect still further disturbances in the occur- 

 rence of faults ; and accordingly we find two very extensive faults on the 

 northern and north-eastern frontier of the Vale of Weymouth, and also two 

 others on the north-west of the Vale of Bredy and near Bridport, besides 

 many minor local fractures. 



The two great faults in the Vale of Weymouth, run nearly in a straight 

 line from east to west, parallel to the general axis of elevation of the whole 

 district, and were probably produced by the same forces and at the same time 

 with this general elevation. 



We shall call the most northerly of them the great Ridgeway Fault, the 

 other the Osmington Fault. Wherever we examine these faults, we find 

 double evidence of the movement that has taken place ; 1st, In the non- 

 accordance of the strata that form the opposite sides of the faults ; 2ndly, In 

 the fine parallel lines and vertical furrows resembling the lines and grooves 

 on Slikensides, and often also in the highly polished surfaces of the materials 

 that form the side walls of the fault, showing that these ponderous masses 

 have ground each other with prodigious violence in the act of separation and 

 movement from their original position. The great Ridgeway fault is an 

 upcast fault, elevating, on its south side, into contact with the escarpment of 

 the chalk strata that would otherwise have dipped beneath it, particularly the 

 Portland stone, nearly along the whole line which this fault traverses. The 

 Osmington fault is a downcast fault, throwing down, on its south side, strata 



* See Plate II. fig, 1, 6. 



f2 



