ON THE OBIGIN OP MOUNTAIN EANGES. 155 



Given that tlio rate of increase of tempoi'ature as wo sink 

 into the earth's crust is 1° Fah. for every sixty feet, and that 

 the average temperature of the surface is 60° Fah., then a 

 pebble or shell at a depth of 600 feet will have a tempera- 

 ture of 50° + 10°, or 60° Pah. Now, suppose 600 feet of sedi- 

 mentary strata to accumulate over this spot ; the pebble or 

 shell will now have a tomporatnro of 60° -f- 20°, or 70° I'ah. 

 It has increased 10° in temperature for the 600 feet of sodi- 

 rnentation. TIius, accompanying the accumulation of great 

 thickness of sedimentary deposits, there is a rise in the 

 temperature of their lower layers. This rise of the isogeo- 

 therms is the starting-point of Mr. Reade's hypothesis. 



For as surely as solids contract on loss of heat, so surely 

 do they expand as their temperature is raised. Prom ex- 

 periments of his own and of others, Mr. lleade takes 2 '76 

 feet per mile as the average expansion increment of rock 

 for every 100° b'ali. Lyell had drawn attention to the 

 vertical uplift due to such expansion. Captain Hutton in- 

 troduced linear horizontal expansion as the main factor in 

 mountain building. But " no one," says Mr. Reado, " so 

 far as I can discover, seems to have perceived in connection 

 with the earth's crust that increase of volume is the final 

 result of expansion. Yet tills must be the most potent of 

 all in its geological effects." 



"Let us now consider," ho says, "what would be the 

 quantitative effect towards the ridging up of a mountain 

 range of a rise of temperature in a given area and depth of 

 rock. Take a volume, for example, equal to 500 x 600 x 20 

 miles ; that is, 5,000,000 cubic miles. If this were heated to 

 a moan of 1,000° Pah., a temperature that must have occur- 

 red over antl over again in the local heating of the earth's 

 crust, there would bo a linear expansion in two directions 

 of 13,760 feet, or 2-6 miles. 



