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Ch. XXXIIL] 



iXD SUBSIDEXCE OF LAXD. 



235 



crusty lias enabled the geologist to infer tliat some of these 

 rocks have been lifted up to the height of several miles above 

 the level at which they were originally formed in the bed of 

 the ocean, and also that there have been gradual subsidences 

 of rocks to a vast amount below the levels which they once 



occupied. 



These 



great movements 



have been caused by 



subterranean or volcanic heat, which has affected different 

 parts of the earth in succession 



The existing mountain 



chains are of different ages, and few of them owe the whole 

 of their present conformation to the movements experienced 

 in a single epoch. The forces, whether in an ujoward or 

 downward direction, to which they are due, and by which the 

 varying position of continents and oceanic basins has in the 

 course of ages been determined, have evidently shifted their 

 points of chief development from one region to another, like 

 the volcano and the earthquake, and are in fact all the 

 results of the same internal operations, to which heat, 



affinity give rise. 



Experiments were made in America, by Colonel Totten, to 

 ascertain the ratio according to which some of the stones 

 commonly used in architecture expand with given increments 

 of heat."^ It was found impossible, in a country where the 

 annual variation of temperature was more than OO"" Fahr., to 

 make a coping of stones, 6 feet in length, in which the 

 joints should fit so tightly as not to admit water between 

 the stone and the cement; the annual contraction and 

 expansion of the stones causing, at the junctions, small 

 crevices, the width of which varied with the nature of the 

 rock. It was ascertained that fine-grained granite expanded 

 with r Fahr. at the rate of -000004825 ; white crystalline 

 marble -000005668 ; and red sandstone -000009532, or about 

 twice as much as granite. 



NOA 



rV 



mass 



temp 



raised 200' Fahr. would lift a superimposed layer of rock to 



'Hier 



level. But, suppose a 

 part of the earth's crust, 50 miles in thickness and equally 



.. ^^l™^^'s American Jonrn. vol. results to the theory of earthquakes was 

 ■ F- 100. I lie application of these first suggested to me by Mr. Babbage. 



m 



