160 



ON THE ORIGIN OP MOUNTAIN RANGES. 



would be 428°5. This assumption is surely bold onougli. 

 And yet in illustrating the results of such expansion on a 

 later page, a mean temperature of more than twice this 

 amount (1,000° Pah.) is assumed. " If this mass oE rock 

 were heated to a mean of 1,000° Fah.," ho says, " a tem- 

 perature that must have occurred over and over again in 

 the local heating of the earth's crust," the results already 

 described would follow. Here the words "increment of" 

 should be inserted before 1,000° Fah., and then we shall 

 perhaps hesitate before admitting that it must have occurred 

 over and over again. If we stick to facts of observation, we 

 have, .say, 40,000 feet of continuous deposit. At an incre- 

 ment of 1° Fah. for every 60 feet of descent (assumed to be 

 constant throughout this depth), this will give us (;6G°G 

 Fah., for the bottom layer, or a mean of 333°3 Fah. for the 

 whole mass. And, as Mr. Fisher has pointed out, these 

 333°3 Fah. have been abstracted from the underlying layers 

 of rock which arc thereby temporarily cooled to that extent. 

 I cannot but think an increment of 1,000° Fah. is, as they 

 say in America, a " little too steep." 



Still, let us accept it for the nonce ; and let us suppose 

 that all the expansion is effective, no part of it being neutra- 

 lised by contraction duo to mctamorphism ; even then we 

 obtain only, on Mr. Roade's showing, a linear expansion in 

 two directions of 2-G miles. J3nt in the Alps Prof. Holm 

 estimates that the compression has been to the extent of 

 seventy-two miles ; and Prof. Glaypolo estimates that in the 

 Appalachian chain, 1.53 miles have been compressed into 

 sixty-five miles. Mr. Reade thinks such estimates excessive. 

 They take no account, or not sufficient account, he thinks, 

 of the squeezing out of the strata where they happen to lie 

 parallel to the advancing plane of pressure, and assume that 

 the tops of the anticlinals were continuous and not cracked, 



