236 Correspondence. 



MR. TOPLEY ON ESCARPMENTS. 

 To the Editor of the Geological Magazine. 

 Dear Sir, — I should not have troubled you with another letter, 

 were it not that Mr. Topley, in your last, unintentionally misre- 

 presents my views so as to make them appear inconsistent. In reply, 

 I shall endeavour to be as brief as possible. 



Bevival of Old Theories. — Mr. Topley regards with disrespect the 

 act of a geologist going back to old times for an explanation of phe- 

 nomena, as if conformity to prevailing fashion in a science were 

 more philosophical than a simple desire for truth. In the history of 

 geology, old fashions have often been revived. The glacial theory of 

 the Parallel Eoads of Glenroy was framed by Agassiz in 1 840, during 

 his Highland tour with Dr. and Mrs. Buckland. It was displaced 

 by the marine theory, which lasted until 1863, when the glacial theory, 

 as explained by Jamieson, received the sanction of the Geological 

 Society. Mr. Topley himself, in his rain theory, has gone back to 

 the days of Hutton and Playfair. The theory of " waves of trans- 

 lation " has found favour with eminent geologists within the last few 

 years, and is still held by Sir Eoderick I. Murchison. I do not think 

 Sir Charles Lyell would object to a wave of translation, such as might 

 be caused by an earthquake capable of upheaving a sea-beach to a 

 height of 40 or 50 feet, or that he would assent to the extreme form 

 in which Mr. Topley has stated his protest against " large bodies of 

 water." 



Lyell on Marine Currents. — I never regarded waves as more im- 

 portant denuding agents than currents, and Sir Charles Lyell, so far 

 from disclaiming the latter, lays the main stress on them. He says 

 (if I rightly remember his words) "the chief influence of the ocean 

 is exerted at moderate depths below the surface, on all those areas 

 which are slowly rising, or are attempting, as it were, to rise above 

 the sea." Currents may have formed the extensive escarpments and 

 terraces revealed by soundings in the Atlantic Ocean, and currents 

 may have commenced those long lines of subaerial escarpment which 

 are rarely paralleled on modem sea-coasts ; but most of the escarp- 

 ments with which I am acquainted show traces of having been at least 

 modified by coast- action. Assuming their littoral origin, England 

 would not be a likely area to present fac-similes of them at the 

 present sea level. Such can only be expected on coasts where the 

 sea is " deep to ;" where it is not prevented, by the task of silting up 

 shallows, from following the strike ; and where, beneath the line of 

 cliff and the influence of waves, there must be a sloping submarine 

 talus of angular materials, similar to that forming the lower part of 

 many inland escarpments. 



So-called Strike Escarpments. — The mode of action assigned by 

 subaerialists to rain and frost involves an entire dependence on 

 structure. Eain and frost can only originate and carry on the work 

 of denudation in conformity to the strike ; but on minute inspection 

 it will be seen that many parts of so-called strike escarpments show 

 a dip along the face of the cliff which proves that the denudation 



