MOVEMENTS AND DEFORMATIONS OF THE EARTH'S BODY. 573 



.000005257 per 1° F., equivalent to .00002838 per 1° C. per volume. 

 In this the proportions of the different rocks in the crust were roughly 

 estimated. To secure an independent result from the best available 

 estimate of what constitutes the average rock, W. H. Emmons has 

 reduced Clarke's average of the chemical constituents of the crust 

 to the norm minerals under the new system of Cross, Iddings, Pirsson, 

 and Washington (see p. 454) and made a weighted average of the con- 

 ductivities of these, as shown in the following table : 



Percentages 

 of norm 

 minerals. 



Sp. Gr. of norm 

 minerals. 



Volume propor- 

 tions of norm 

 minerals. 



Volume propor- 

 tions of temp. 

 1° C. higher. 



Quartz 



Feldspars ^ . 

 Diopside . . . 

 Hypersthene 

 Magnetite . . 



Total. . 



11.4 

 62.3 



6.8 

 10.2 



6.8 



97.5 



2.66 



2.7 



3.3 



3.45 



5.17 



4.2801548504 

 23.0703582771 

 2.0600482040 

 2.9500722750 

 1.3000372060 



33.66 



33.6606708125 



Subtracting the stated volume from the volume at a temperature of 

 1° C. higher, the difference is found to be .0006708125, which divided 

 by the volume gives .0000199, which is the coefficient of expansion of 

 the theoretical, average, surface rock of the earth. 



With this coefficient, the radial shrinkage resulting from an average 

 loss of 10° C. (18° F.), (Tait's estimate), is a little over a quarter of a 

 mile (.2572); and for a loss of 45° C. (81° F.), (estimate of DanielFs 

 Physics), a httle over a mile (1.1574). The shortening of the circum- 

 ference for 10° C. loss is 1.6 miles, and for 45° C, 7.27 miles. Com- 

 putations based on the coefficient of expansion adopted by Reade 

 give 2 . 35 miles circumferential shortening for a loss of 10° C. and 10 . 5 

 miles for a loss of 45° C. In both these cases, the whole contraction 

 is assumed to take a vertical direction, and hence these are maximum 

 results. They are exceedingly small. 



Unless there is a very serious error in the estimated rate of thermal 

 loss, or in the coefficients of expansion, cooling would seem to be a ver}^ 

 inadequate cause for the shrinkage which the mountain foldings, over- 

 thrust faults, and other deformations impty. This inadequacy has 



^ All the feldspars are calculated as anorthite. Augite is used for hypersthene, 

 ilmenite is included with magnetite, and all minerals are calculated as if of the isometric 

 system. 



