1852.] WESTON ON THE UPWAY VALLEY. 115 



23. Besides the dip to the N., this section points to a fall of the 

 strata coinciding with the surface-dip of the country. 



General deductions to he drawn from the sections unitedly. 



These in the aggregate (with few exceptions) give on both sides of 

 the valley a dip to the N., and even the apparently anomalous sections 

 (14, 15, and 16) do not in any way affect the main question, because 

 the strata of that part of the Purbeck series which really forms the 

 Up way Valley, have the same normal bearing. The local subsidence 

 of the strata lies in fact beyond the limits of the valley. 



The Purbeck beds have been shown to crop out along the base of 

 the northern range, and then to cap the southern, just in the natural 

 direction of the strata when they were continuous. 



The capping consists of outliers of the Ridgway Purbeck beds, — 

 or rather, is an almost unbroken extension of those beds from Upway 

 to the termination of the Portland range at Portisham. 



The valley does not present any symptoms of longitudinal disturb- 

 ance, but, as far as observation extends, discloses in its hollow such 

 different parts of the \Vealden and Upper Oolitic rocks as we should 

 ^priori expect to find. 



We may therefore infer conclusively that the strata of the Upway 

 Valley have been cut down to their present level by aqueous abrasion. 

 The valley is strictly a valley of denudation. 



The general evidence of all the sections and the vertical section 

 right across the valley, given under sect. 17, concur in proving that 

 the great section of the Ridgway cutting (fig. 8) may be considered 

 a type of the common structure of the Upway Valley. 



Sect. 23 [not on the map, — it is to the S. of, and close by, the 

 farmhouse] is N. of sect. 1, and these two have a coincident dip 

 forming the depression near the farm-house. This depression I found 

 barometrically to be about 60 feet below the level of the same strata 

 in the Ridgway cutting. Sections 19 and 1 show also dips in oppo- 

 site directions, so that sect. 19, together with 1 and 23, indicate re- 

 spectively the W. and E. extremes of a geological arch, and point 

 to the E. part of the valley as a locality of disturbance. The de- 

 pression near the farm is therefore what I hesitatingly suggested in 

 1848, "not merely external, but essentially connected with the stra- 

 tification below." 



Fig. 9. — Diagram showing the arched strata between the old Ridg- 

 way Road and the Farmhouse, and exhibiting the region of 

 the greatest disturbance at the base of the Ridgway Range. 



N.N.W. S.S.E. 



Old Road. South of Farmhouse. 



(Sect. 19.) C (Sect. 23.) 

 A. 



Level. B 



The arc, A C B, approximately represents the arched strata of Purbeck, and the 

 chord, A B, the relative difference of level of the two extremes. B therefore 

 shows the local subsidence. The flexure of the strata, as stated in the details 

 already given, increases from A to C, and then in a more rapidly increased ratio 

 from C to B. 



i2 



