Elevation and Subsidence of the Surface of the Earth, 405 



ately after deposition, and therefore the expansion which must 

 necessarily follow the formation of thick deposits would throw 

 it into anticlinal ridges. The same would occur with incoherent 

 rocks when they were covered up with limestone — with this dif- 

 ference, however^ that the amount of lateral pressure developed 

 would be limited by the weight of the superincumbent deposits. 

 The deposition of limestone, therefore, relieves the pressure,while 

 the deposition of sand and clay increases it. 



The following Table exhibits approximately the height, in feet, 

 of the anticlinals caused by an accession of heat to rocks forming 

 the surface of a sphere with a radius of 3956 miles, the rock 

 being supposed to expand in length "000005 for each degree of 

 temperature. The upper line shows the thickness, in feet, of the 

 deposit necessary to raise the temperature the number of degrees 

 indicated in the second line from the top. The left-hand column 

 shows the breadth of the anticlinal in miles. 



Thick. 



500 ft. 



1000 



1500 



2000 



2500 



5000 



10,000 



15,000 



20,000 



25,000 



Temp. 



10°. 



20°. 



30°. 



40°. 



50°. 



100°. 



200°. 

 feet. 



300°. 



400°. 



500°. 



Dist. 

 miles. 



feet. 



feet. 



feet. 



feet. 



feet. 



feet. 



feet. 



feet. 



feet. 



100 



1140 



1950 



2550 



3100 



3700 



5,650 



8,700 



10,900 



12,700 



14,6001 



200 



1200 



2600 



3700 



4650 



5500 



9,200 



14,700 



19,300 



22,700 



25,100 ! 



300 



1450 



2850 



4250 



5300 



6350 



11,400 



19,100 



25,400 



33,100 



36,800 



400 



1530 



3000 



4350 



5800 



7050 



12,860 



21,650 



30,160 



37,470 



43,400 



500 



1550 



3050 



4500 



5900 



7220 



13,200 



24,200 



33,400 



41,550 



49,300 



1000 



1570 



3080 



4650 



6150 



7700 



14,500 



28,600 



41,700 



53,750 



65,400 



2000 



1900 



3200 



4700 



6250 



7800 



15,400 



30,700 



45,600 



57,300 



74,400 



It appears from this Table that deposits no thicker than we 

 know some formations to be, spread over areas of moderate 

 extent, are capable, under favourable circumstances, of producing 

 higher mountains than any we know at present ; but it will be 

 noticed that this operation will only take place on an extensive 

 scale if the rate of heating from below is slower than the rate 

 of deposition from above ; for if such were not the case, the 

 elevation would follow so quickly after the formation of the lime- 

 stone that no very thick deposit could be formed before the bed 

 was raised to the sea-level. If, however, deposition took place 

 more rapidly than the conduction of the heat outward, large 

 deposits would be formed, which would be below the normal 

 temperature due to their depth from the surface; and these 

 therefore would continue to expand, and therefore to rise, until 

 their normal temperature was attained; and the greater the 

 difference between the rates of deposition and conduction, the 

 greater would be their ultimate height. It is therefore ne- 

 cessary to examine this point. 



