Correspondence. 185 



situations," or indeed along the borders of any submerged areas " not 

 open plains." 



I find no mention of ordinary marine action in this part of Mr. 

 Mackintosh's letter, other than the supposition that "transverse 

 gorges" may have been finished by "marine currents." Such 

 transverse valleys it is admitted " may have been partly excavated 

 by streams flowing down once continuous slopes." Eain and frost 

 are rejected by Mr. Mackintosh as sufficient agents for the denu- 

 dation of the valley systems referred to ; but, he adds, " It must 

 have been a toholesale denudation, and not a denudation by instal- 

 ments. Large bodies of water in the shape of marine currents, or 

 " waves of translation," caused by sudden elevations, ought not, I 

 think, to be rejected as a cause, until their inadequacy has been 

 clearly shown." 



I think, Sir, your readers will have perused the foregoing assertion 

 with no little surprise, remembering that Mr. Mackintosh originally 

 commenced this discussion as an avowed advocate of Sir Charles 

 Lyell's theory, that escarpments are old sea-cliffs, formed by 

 ordinary coast action. Now, it should not be forgotten that both 

 Sir Charles Lyell, in advocating marine action, and the " sub- 

 aerialists," in advocating atmospheric-action to account for the 

 origin of escarpments, alike appeal to causes noiv in action, the 

 effects of which are known. This is the chief lesson which the 

 works of Sir Charles Lyell have taught geologists, and subaerialists 

 in urging " rain and rivers " as denuding agents are consistently 

 following out his philosophy. But when ideas are introduced 

 wholly unknown to modern science, such as "large bodies of 

 water," "waves of translation," etc., the discussion is at once carried 

 back to geological controversy, as it existed before the publication 

 of the "Principles of Geology." I think the sentence quoted above 

 should read thus, and I am sure Sir Charles Lyell would fully agree 

 with my rendering — " Large bodies of water in the shape of marine 

 currents, or 'waves of translation,' (however produced), ought not 

 to be admitted as a cause, until their adequacy, (or, at least, their 

 possibility,) has been clearly shown." 



Upon Mr. Mackintosh's further suggestion that, in the event of 

 such diluvial action being found untenable, " equally great bodies of 

 moving ice " may prove satisfactory, I need say nothing. It apparently 

 belongs to the same cataclysmic class of agencies as the former. 

 The claims of Ice, in a moderate and reasonable form, have already 

 been advocated in your pages by the Eev. 0. Fisher (Nov. 1866) ; 

 and if Mr. Fisher is prepared to show that Glacial action in com- 

 paratively modem (geological) times, has been universal over the 

 globe, as we Imoio escarpments to be, the idea might be worthy of 

 consideration, as indicating a probably important agent in modify- 

 ing, if not in originating, escarpments. But it is unwise to accept 

 agencies of limited applicability to explain universally occurring 

 phenomena, when we have agencies everywhere active, and which 

 are believed, given sufficient time, to be equal to the work performed. 



In a footnote at p. 137, Mr. Mackintosh refers to a paper by me on 



