480 Correspondence—Mr. T. Mellard Reade. 
used measures of the maximum thicknesses, I have considered that 
these would in all probability not differ much from the original 
average thicknesses of the same rocks before they had suffered denu- 
dation. No doubt some rocks may have been wholly destroyed by 
denudation, or are so covered up by later deposits as to be beyond 
our reach, and to allow for these 1 am willing to admit that my 
estimate of the whole thickness of the rocks, and therefore of the 
time taken to produce them, may have to be considerably increased ; 
but this would bring my figures nearer to those usually arrived at, 
not enormously further from them as Mr. Reade endeavours to prove. 
Yet again, Mr. Reade points out that continents have fluctuated, 
and have sometimes. been larger than now. To allow for this he 
doubles the land surface and reduces the corresponding thickness of 
the strata to one-half! But, surely, if the continents have been 
sometimes larger, they have also been sometimes smaller, and I see 
no reason to think we can take any fairer average than that of the 
present area; and even if the average had been double, then the 
denudation and the deposit would presumably have been double also, 
not half as Mr. Reade suggests. 
With regard to my fundamental position—that the areas of 
deposition are (and always have been) very much smaller than the 
areas of denudation, and that, in making any estimate of geological 
time founded on the thickness of the sedimentary rocks and the 
known rate of denudation, this fact must be taken account of, Mr. 
Reade makes no objection; and, whatever ‘confusion of ideas ” 
may have pervaded my estimate, the subject has certainly not been 
rendered clearer by his criticism. 
Finally, as regards the general theory of the ‘“‘ Permanence of 
Oceans and Continents” (or, more properly, of Oceanic and Con- 
tinental areas), which Mr. Reade somewhat sneeringly remarks ‘is 
now becoming fashionable,”’—it is time that its opponents should 
give up petty criticism of unimportant details or collateral issues, 
which have little bearing on the main question, and attempt to 
grapple with the whole body of facts and arguments adduced in its 
support by some of the first geologists of the day, and which I have 
endeavoured to set forth in a connected form in the pages of “Island 
Life.” Any such general examination of the question from an 
adverse point of view, I have hitherto failed to meet with. 
ALFRED R. WALLACE. 
THE OLD HYTHE PINNACLE OF CHALK. 
Str,—On referring to the Life of Lyell, I find the letter relating 
to the disappearance of the Old Hythe Pinnacle of Chalk was written 
in 1869, not 1864. The evidence of Lyell does not therefore con- 
flict with that of Prof. Seeley and Mr. Searles Wood, as I thought 
it did, but taken with theirs, rather points to the total destruction of 
the pinnacle between those dates. With this correction I must close 
the correspondence on this subject so far as I am concerned. 
T. MeLuarp READE. 
Sept. 4, 18838. 
