Correspondence. 571 



LYELL, JUKES, AND WHITAKER ON SURFACE-GEOLOGY. 



To the Editor of the Gteological Magazine. 



Sir, — Since I last wrote very briefly on the origin of escarpments/ 

 you have admitted into your pages two articles, one by Mr. Whitaker, 

 and one from Professor Jukes, which, were they to remain unnoticed, 

 might leave the controversy too one-sided, more especially as the 

 first-named author has spoken in very strong and persuasive terms 

 (coupled with a grace and elegance which remind one of the illus- 

 trious Playfair), which are calculated to mislead those who have not 

 studied the other side of the question. 



I/yelVs Becantation. — Let me fixst call attention to a change of 

 opinion in the great fomider of inductive geology — Sir Charles Lyell, 

 as announced by Mr. Whitaker. Ordinary coast-action, Sir Charles 

 now believes, will not accoimt for the parallelism of the Chalk and 

 Greensand escarpments, or for both following the strike of the strata. 

 But to reject coast-action as the main or primary cause of these 

 escarpments is not entirely to give up the marine theory ; for they 

 may have originated in longitudinal cracks during axial elevation, 

 and may afterwards have been deepened and widened, and their 

 inner sides planed down by currents maintaining a general uniformity 

 of direction, but at intervals deflected and reflected so as to hollow 

 out the cuimlinear " coves " by which the " capes " are separated.^ 

 But suppose it could be shown that powerful currents, operating at 

 a considerable, not "too great" a depth, are incapable of scooping 

 out the depressions bounded by escarpments, it would not be more 

 inconsistent with uniformity to suppose a cyclically-reciuring in- 

 tensification of the action of currents, caused by sudden upheavals of 

 strata, than to admit " occasional strides, constituting breaks in the 

 otherwise continuous series of (organic) changes." ^ 



Whitaker on Chalk Escarpments. — Mr. Whitaker and other sub- 

 aerial geologists, though they have thrown difficulties in the way of 

 the marine theory, have brought forward very few facts in support of 

 their own views. The main force of what they have advanced lies 

 in a few words — Because sea-coast action could not have done it, 

 therefore it has been done by rain and frost. To state that a river 

 sometimes flows near the base of an escarpment, coupled with the 

 admission made by Messrs. Foster and Topley, and implied by Mr. 

 Whitaker, that escarpments are not river-clifis — ^that springs are 

 often found at the base of escarpments — and that time will accom- 

 plish anything . . . cannot be regarded as evidences, imless it can 

 be shown that these agents are now actually giving rise to phenomena 

 similar to those requiring explanation. An escarpment is a steep, 

 continuous slope. Continuity, both longitudinally and transversely, 

 are its essential characteristics. Springs, at intervals, cause landslips 

 which break this continuity, and therefore tend to destroy escarp- 

 ments. Kain- streamlets (where they are not prevented by a covering 



1 Geol. Mag. May, 1867. 



2 See reference to escarpments under the Atlantic, ibid. p. 236. 

 ' Lyell's Antiquity of Man. 



