62 BihliograjpMcal Notice. 



Fig'. 4. P. Sancti-Patriciz : a, riglit valve ; b, dorsal aspect. 

 Fig. 5. Cythere Wrightiana : «, left valve ; h, ventral view. 

 Fig. 6. C. JBailyana : a, right valve ; h, dorsal view. 

 Fig. 7. C. Jukesiana : «, right valve j 6, ventral aspect. 

 Fig. 8. C Harknessiana : a, right valve ; h, dorsal aspect. 

 Fig. 9. Bairdia Murehisoniana : a, left valve ; 6, ventral view. 

 Fig. 10. jB. Griffiihiana : a, left valve j &, ventral view. 

 Fig. 11. ^. Salteriana: a, right valve j 6, ventral view. 

 Fig. 12. Cythere Aldensis : right valve. 



BIBLIOGKAPHICAL NOTICE. 



On Subaerial Denudation^ and on Cliffs and Escarpments of the 

 Chalk and the Lower Tertiary Beds. By William Whitaker, 

 B.A., F.G.S., &c. 8vo, pp. 27. Hertford, 1867. 



" Foe some years," writes Mr. Whitaker, in this reprint from the 

 * Geological Magazine, " geologists have more or less agreed in the 

 view that the present features of the earth, whether hiU, valley, or 

 plain (with some small exceptions, as volcanic outbursts), have been 

 formed directly by denudation; though indirectly disturbances, 

 whether faults, upheavals, or sinkin-^s, have of course ha^^ their 

 effect in determining the flow, so to speak, of the denuding agent." 



Of late much discussion has been held on the corcparative effect 

 of the two forces, disturbance and denudation, and on the relative 

 extent to which sea- action on the one hand and atmospheric agen- 

 cies on the other have worn away the earth's surface and carved its 

 rocks into their present form. 



Although the action, simple or combined, of frost, avalanches, 

 glaciers, icebergs, coast-ice, river-ice, rain, snow-water, springs, 

 torrents, and rivers, has never been ignored by geologists since their 

 science took a systematic form, yet doubtless they have been too 

 much influenced in general by the popular notion that the sea has 

 been up and over the land time after time, and effected the scoop- 

 ings and carvings of hill and valley, — the quiet and slow action of 

 air and rain (universal, indeed, but lost sight of by the unobservant) 

 having been neglected in many calculations as to the alterations 

 the earth's surface has undergone. Now that advanced knowledge 

 and improved observadon have given credit to atmospheric agencies, 

 rather than to marine action, for some of the enormous denudations 

 recognized by geologists in past as well as in present times, we are 

 not at all surprised to find some favouring the new views with such 

 warmth as reaction, enthusiasm, and party-feeling usually create. 

 With an earnest love of truth and of his subject, the writer of this 

 pamphlet has carefuUy collated the statements of many geologists 

 about " subaerial denudation," showing how much has already been 

 done and thought on the subject ; and he adds his own experience 

 and views, somewhat dogmatically and with some contempt for those 

 whom he regards as differing from him. 



