XXVlll 



Apppudix. 



rock, could only be relieved by the whole stratum bulging upwards and 

 forming an arch, or more properly a dome ; and as we know the rate of 

 expansion, we can calculate what the elevation would have to be on a sphere 

 the size of the earth, for various temperatures and for different areas, in order 

 to relieve the pressure. This is exhibited in the following table, which is part 

 of a larger table that I have calculated.'^ In it the upper line is the thickness 

 in feet of the deposit, while the second line is the temperature due to that 

 thickness. The left-hand column is the diameter, or breadth, in miles of the 

 heated area, while the other columns show the elevation in feet that would 

 take place : — 



Thickness 



500 feet 



2,500 feet 



10,000 feet 



25,000 feet 



Temperature ... 



10' 



50° 



200^ 



500=^ 



Breadth, 100 miles 



1,140 feet 



3,700 feet 



8,700 feet 



14,600 feet 



„ 500 „ 



1,550 „ 



7,220 „ 



24,200 „ 



49,300 „ 



., 1,000 „ 



1,570 „ 



7,700 „ 



28,600 „ 



65,400 „ 



„ 2,000 „ 



1,900 „ 



7,800 „ 



30,700 „ 



74,400 „ 



From this table it will be seen that formations no thicker nor more 

 extensive than those that we know to have been deposited, are quite capable 

 of being elevated far above the highest known mountains. 



It may have occurred to you that a bed of limestone would not be capable 

 of supporting itself as an arch, and, therefore, that instead of being elevated 

 it would break up into fragments ; this is very true, if the arch was entirely 

 unsupported, but as soon as the expansion overcame the rigidity of the crust, 

 and movement commenced, the underlying superheated rocks, being relieved 

 from pressure, would rise up and still press upwards on the rising arch, so 

 that the pressure expended in elevation w^ould be that capable of overcoming 

 the rigidity only of the crust, and not its weight. You may also have 

 noticed that unless the rate of deposition was greater than the rate of the 

 conduction of heat outwards, no deposit would rise above the surface of the 

 sea, for as soon as deposition ceased the increase of temperature would cease 

 also ; and conversely, the greater the difference between the rates the greater 

 would be the rise, for the longer would be the time before the deposit attained 

 its normal temperature. 



The data to estimate these rates are not very exact, more especially the 

 rate of deposition, but the following is the best information that I can 

 collect : — 



Monsieur Joseph Fourier has calculated that the earth decreases in tem- 



* This table is calculated on the suppositions that the earth is a sphere, with a radius 

 of 3,956 miles, and that rocks expand -000005 for 1° Fahr. 



