110 proceedings of the geological society. [jan. 21, 



January 21, 1852. 



The following communications were read : — 



1. On the SuB-ESCARPMENTS of the Ridgway Range, and their 

 Contemporaneous Deposits in the Isle of Portland. By 

 Charles Henry Weston, Esq., Barrister-at-Law, B.A. Cantab. 

 F.G.S. 



Since I had the honour of presenting to the Geological Society some 

 remarks on the nature and superposition of the formations at Ridg- 

 way*, I have had another opportunity of examining that locality, and 

 the following are the conclusions to which I have been led. 



1. That the entire valley of Up way, although disturbed, is yet one 

 of denudation and not a synclinal trough, as hitherto considered. 



II. That the section of the Ridgway cutting f exhibits, more or 

 less, the normal structure of the whole range. 



III. That my views respecting the extension of the Purbeck group 

 to the most westerly limits of the Gorton Hill J and Whaddon Ridge, 

 have been confirmed ; and 



IV. That the same Formation, on the other side of the great anti- 

 clinal axis of this district, does not terminate at the centre of the Isle 

 of Portland, but exists also at the Bill, its most southerly point. 



Before entering upon the subjects under consideration, it will be 

 necessary to bear in mind that the elevated land of Ridgway bounds 

 the Upway Valley on the north side, and is composed of local patches 

 of tertiary deposits, and of chalk and greensand, with subjacent 

 "Wealden and Upper Oolite ; while parallel to this, on the south 

 side, ranges a steep Hogsback, consisting of the Purbeck and Upper 

 Oolitic groups only. This southern ridge, although evidently once 

 continuous, is now cut through by transverse gorges and valleys, (See 

 Map, fig. 1) resulting, as the geological features of the country seem 

 to indicate, from long-continued action of the then existing sea. 



The following selected sections on the southern sub-escarpment will 

 be sufficient to convey an idea of the internal structure of this range. 

 They commence a little east of the railway embankment, and are to 

 be found as we proceed westward to its termination near Portisham. 



1 § . Portland Oolite (with Ammonites and Trigonice) : double dip. — 

 One to N.by W. at the high angle of 40°, and the other to N.E.by 

 E. at 20°. The valley in parts cut down to the Portland sand. 



2. The Purbeck and Portland formations are here brought into 

 juxtaposition, as shown in the diagram, fig. 2. 



3. Crest of hill.— Pwr^ec^-: dip to N.N.E. at 20°. Upway Valley 

 apparently cut down to the Portland oolite. 



4. Crest of hiW.—Furbeck : dip to N. by E. at 20°. 



* Quart. Journ. Geol. Soc. vol. iv. p. 245, and vol. v. p. 317. 

 t See also Quart. Journ. Geol. Soc. vol. iv. p. 249. 

 X Quart. Journ. Geol. Soc. vol. v. p. 318. 



§ The numbers refer to the sections marked on the ground-plan of the district, 

 given in the Map, fig. 1 . 



