86 SURVEY UNDER OFFICE OF WORKS CHAP, in 



Wales, the illustrations of which are most beautiful, and with nine- 

 tenths of which, in regard to the conclusion and reasonings, I agree. 

 I shall have to cite it in a seventh edition of my Principles, which 

 I am now printing, and I wish to guard myself against misunder- 

 standing the only point on which I shall have to differ from you. 

 I am anxious to have a speedy answer, as the sheet in which I shall 

 allude to your paper will soon go to press. 



In that part of your section, plate 4, which relates to the Mendip 

 region, one which I have gone over sufficiently to take more interest 

 in it than I otherwise should do, you mean to say, if I mistake not, 

 that between 4000 and 5000 feet of strata have been removed by 

 denudation, between C and 40 ; in other words, that between the 

 deposition of certain Carboniferous strata and certain newer beds, 

 40, two events occurred : first, the disturbance of the beds of the 

 Palaeozoic rocks ; second, the denudation of several thousand feet of 

 the same beds. Yet it seems to me, on reading other passages of your 

 paper, that you cannot mean this; for your ideas of denudation 

 acting contemporaneously with subterranean movements, whether 

 of upheaval or depression, agree with those which I published in 

 1831 in my Principles (and, by the way, before that time it was 

 thought a triumphant argument against what were called 'modern 

 causes' to prove that a river could not denude the rocks); the 

 gradual action of the ocean acting concurrently with movements 

 of the land, as exemplified in my denudation of the Wealden, had 

 not, so far as I know, been fully set forth in any geological work, 

 with due allowance also for the resistance of the harder and yield- 

 ing of the softer rocks. 



Now as you adopt these views, and have applied them with all 

 the modern lights to your sound and philosophical speculations in 

 this essay, I cannot comprehend how you can dispense with in- 

 definite geological time for your denudation in the case I allude 

 to. But if so, what becomes of your argument at p. 317 in favour 

 of grand catastrophic and intense disturbing power between the 

 close of the Coal Measure Period and the deposition of the un- 

 conformable beds, 4*2 ? You must be well prepared, from what I 

 have said of the amount of denudation, especially in my Elements, 

 for my willingness to admit as much of it, or more than you want, 

 as it must have exceeded all the sedimentary strata which are a 

 measure of its quantity, and of the gradual manner or slow rate at 

 which it took place. You will also expect that I, at least, shall feel 

 no difficulty in granting an indefinite lapse of geological time 

 between the deposition of the last of the Coal Measures in the 

 Mendip region and the oldest of the overlying conglomerates of 

 that country. The entire flora and fauna were changed once, if not 

 more, during that interval of unknown extent, and therefore I have 

 no objection to as much elevation, disturbance, and denudation as 



