Notices of Memoirs — Rutton, on Mountains. 171 



half millions of years ago. From that time to the present, elevation 

 must have gone on in an increasing scale ; but, although increasing 

 in height, it must have also been decreasing in rapidity, and a time 

 must inevitably arrive when elevation will be so slow that it will do 

 no more than equal denudation, and when again, 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 5,400 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 8,400 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 Nummulitic 

 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, Himalayas, 

 and the mountain chains of Persia ; we find, in fact, that the area of 

 the Nummulitic 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 Nummulitic Formation. A thickness of 15,000 feet of limestone 

 over an area 1,800 miles in breadth is also more than sufficient to, 

 elevate into the air the most towering peaks of the Himalaya. 



1 I need hardly say that these numbers are introduced as an illustration merely, and 

 make no pretension to accuracy. 



