62 Bibliographical Notice. 
. P. Sancti-Patriei: a, right valve; 6, dorsal aspect. 
. Cythere Wrightiana: a, left valve; b, ventral view. 
. C. Bailyana: a, right valve; 6, dorsal view. 
. C. Jukesiana: a, right valve; 6, ventral aspect. 
. C. Harknessiana: a, right valve; 5, dorsal aspect. 
. Bairdia Murchisoniana: a, left valve ; 6, ventral view. 
Fig. 10, B. Griffithiana: a, left valve; 6, ventral view. 
Fig. 11. B. Salteriana: a, right valve; 6, ventral view. 
Fig. 12, Cythere Aldensis: right valve. 
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BIBLIOGRAPHICAL NOTICE. 
On Subaérial Denudation, and on Cliffs and Escarpments of the 
Chalk and the Lower Tertiary Beds. By Wiui11amM WuitakEr, 
B.A., F.G.S., &. 8vo, pp. 27. Hertford, 1867. 
« For some years,” writes Mr. Whitaker, in this reprint from the 
‘Geological Magazine, “ geologists haye more or less agreed in the 
view that the present features of the earth, whether hill, valley, or 
plain (with some small exceptions, as volcanic outbursts), have been 
formed directly by denudation; though indirectly disturbances, 
whether faults, upheavals, or sinkings, have of course hau their 
effect in determining the flow, so to speak, of the denuding agent.” 
Of late much discussion has been held on the comparative 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 observation 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 carefully collated the statements of many geologists 
about “ subaérial 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. 
