XXX Appendix. 
therefore, no more land can rise much above the surface of the sea. Now, 
it has been estimated that a foot of soil is removed by denudation in from 
500 to 12,000 years, according as the land is mountainous or level, and if we 
take the lowest estimate as that which will be nearest to the conditions at the 
time I am talking about, we find that the interior heat would have to increase 
at the rate only of 1° in 10,000 feet to bring about the result.* This, by 
Sir W. Thomson’s theory, will not be for thirteen billions of years; so 
that the earth is but in its infancy between birth and the repose of old age, 
and we have plenty of time to look forward to for improvement and 
development. 
But leaving these speculations, it is, I think, time that I gave you an 
illustration of the theory. I select the Wealden District in the South of 
England. This district extending through Kent, Sussex, and Hampshire, is 
formed by an anticlinal curve of the cretaceous and wealden strata. The 
thickness of the beds is 3,400 feet, and the highest part of the arch would 
have attained, if the upper portion had not been denuded off, a height of 
about 3,600 feet above the sea. The base of the arch below London is about 
500 feet below the sea, so that the total rise of the arch must have been 
about 4,100 feet, while the breadth of the anticlinal from London to some 
point in the English Channel is about 100 miles; these, therefore, are our 
data. Now a thickness of 3,400 feet implies an elevation of temperature 
of 68°, and this over a breadth of 100 miles would give an elevation of 4,650 
feet, that is to say 150 feet more than the actual rise. But as the land rose 
above the sea denudation would commence to work upon it, so that the 
temperature would not be able to rise the whole 68°, and this will account for 
the 150 feet which the anticlinal arch failed to attain. 
I will give you another and more general illustration. During the Eocene 
period a large ocean, at least 5,000 miles long by 1,800 broad, extended over 
the south of Europe and the north of Africa, and was continued eastward 
through Asia Minor, Persia, and Northern India to China, In this ocean, 
what is known as the mummulitic limestone was formed to a thickness of 
15,000 feet. Consequently if, as I have said, large limestone deposits produce 
elevation, it is here that we ought to find the evidence of it; and this we 
plainly do in the Atlas, Pyrenees, Alps, Apennines, Carpathians, Himalaya, 
and the mountain chains of Persia ; we find, in fact, that the area of the 
mummulitic limestone embraces the most mountainous country in the world, 
and geology shows us that these mountains are all about the same age, and 
all have been elevated since the period of the mummulitic formation. A 
thickness of 15,000 feet of limestone over an area 1,800 miles in breadth is 
* I need hardly say that these numbers are introduced as an illustration merely, and 
make no pretension to accuracy. 
