112 



PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Jan. 21, 



8. Crest of hill.— Purbeck : dip to W. at 5°. 



9. Crest of hilh—Purbeck (2 quarries) : dip to N.E., 5°-10°. 



Fig. 2. — The Fault seen at Sect, 2. 



Purbeck. 



■ ■s^S 



Portland 



Observations on the sections of the southern sub-escarpment. 



1 . Shows not only the greatest inclination of strata in a direction 

 generally common to the entire range, but also a co-existing dip to 

 the E. This section exhibits a local subsidence. 



1 to 9. Show in the aggregate a gradual decrease of dip from E. 

 to W., evidencing sect. 1 . as marking the region of the greatest dis- 

 turbance (see fig. 9). 



2. Shows a downcast fault ; an examination, however, of the whole 

 range leads to the conviction that this is not the result of disturbance, 

 strictly so called, but rather of a slip occasioned by the subtraction 

 of part of the Kimmeridge clay (on which the hill is based), by the 

 action of the then contiguous sea. This forms one of the indications 

 before alluded to, of the continued nature of the water-action then in 

 operation. 



5. In this quarry, amidst the lines of black flinty masses, which 

 so characterize the Portland oolite, I found wood partly silicified and 

 partly retaining carbonaceous matter, as well as the remains of a tree, 

 apparently exogenous, about 18 inches in diameter. 



2 to 9. Show that wherever the crest of this entire southern ridge 

 has not been denuded, the Purbeck is found resting conformably 

 ujpon the Portland oolite as far as its most westerly limit. 



The western extremity of the valley has very little depth and rather 

 merges in the hills. In denudation, we may consider the valley as 

 affected to the Purbeck in the west ; further east, to the Portland 

 oolite-, and at section 1, to the Portland sand \ i. e. it appears to 

 deepen progressively from west to east ; this is illustrated by the ac- 

 companying diagrams (figs. 3, 4, 5, and 6). Sections 6 and 7 do not 

 negative this conclusion, because these refer to the N. and S. transverse 

 gorges, and not to the great Upway Valley at right angles to them. 



We have now to examine the base of the chalk-range on the north 

 side of the Upway Valley, and I shall subjoin (in brief) such sections 

 as are necessary to render intelligible its stratigraphical details, taking 

 an opposite direction, from west to east, and ending on the east at 

 the farmhouse north of section 1 . 



10. Purbecky containing apparently Cyrena or Cyclas : dip not 

 visible. 



