120 Henry Bury — Escarpments and Transverse Rivers. 



to have a deep byssal notch below it. The posterior margin of the 

 posterior ear meets the hinge-line at a very obtuse angle. The 

 surface of the body has a few strong, but low, concentric undulations 

 and finer concentric lines. Wheelton Hind ' considers Von Koenen's 

 species to be identical with Salter's Avicidopecten fibrillosus, which 

 he j)uts in the genus Pseudamusium. Ps. auriculatmn (McCoy) ^ 

 may also be compared. 



Avicidopecten cf. densistria (Sandberger). (PL II, Fig. 9.) 

 The right valve of a small pectinif orm shell, of which the impression 

 and external cast are preserved, is practically indistinguishable 

 from the Culm species described and figured by Von Koenen® 

 as Pecten densistria Sandberger.'' Our specimen has a height of 

 about 6 mm. and a width of about 5 mm. 



Actinopteria sp. 



The impression of the left valve of a small shell, about 9" 5 mm. in 

 length, appears to belong to the genus Actinopteria or Pteronites. 

 In general shape, position of beak, size of pre-umbonal portion, 

 hinge-line, and convexity of body, it resembles the Scotch species, 

 Pteronites flixtuosus Etheridge,^ which Hind ^ refers to the genus 

 Actinopteria, but the ornamentation is rather different, con- 

 sisting in our specimen of numerous very fine, equidistant, regular 

 radiating lines, more closely placed on the flattened posterior half 

 of the shell behind the body, on which concentric growth- lines are 

 also present. 



[To be continued.) 



Escarpments and Transverse Rivers. 



By Henry Bury, M.A., F.G.S. 



AT the end of a valuable paper on the superficial deposits to the 

 north and north-west of London, Mr. Barrow '' puts forward 

 certain views as to the origin of escarpments and transverse rivers 

 in the Chiltern Hills and the Weald which can hardly be allowed 

 to pass unchallenged by those interested in the progress of geo- 

 morphology , for unless there is more evidence in their favour than has 

 yet been produced these views are not progressive, but distinctly 

 reactionary. To sum up the position in his own words (op. cit., 

 p. 47) : " Long after the cessation of all the bending movements 



1 Wheelton Hind, op. cit., vol. ii, 1903, p. 106, pi. xvi, figs. 16-22. 



2 Ibid., p. 108, pi. xvi, figs. 23-7. 



^ Von Koenen, op. cit., p. 327, t. vi, fig. 2. 



^ Sandberger, Rhein. Schichtsyst. Nassau, p. 296, t. xxx, fig. 12. 



* Etheridge, Geol. Mag., Vol. X, 1873, p. 345, PI. XII, Fig. 1. 



6 Wheelton Hind, op. cit., p. 25, pi. v, figs. 8-12. 



'' Proc. Geol. Assoc, vol. xxx, 1919, pp. 1-48. 



