246 SEE— FURTHER RESEARCHES ON [April 24, 



fastest; but there would inevitably, sooner or later, come a time when the 

 exterior, receiving heat from abroad (sun and space), as well as from 

 within, would assume an almost constant temperature, while the interior 

 would still continue to cool, and contract. Thus, therefore, after a while 

 the interior nucleus would contract faster than the exterior shell. It would 

 do so, partly because it would cool faster, and partly because the coefficient 

 of contraction of a hot body is greater than that of a cooler body. Now, as 

 soon as this condition was reached, the exterior shell, following down the 

 shrinking nucleus, would be thrust upon itself by a lateral or horizontal 

 pressure which would be simply irresistible. If the earth's crust were a 

 hundred times more rigid than it is (thirty times as rigid as steel, 500 to 

 1,000 times as rigid as granite — Woodward, Scioice, Vol. XIV, p. 167, 1889), 

 it must yield. Mountain-ranges are the lines along which the yielding takes 

 place, and this yielding takes place along the lines of thick sediments be- 

 cause these are lines of weakness. 



"There are several serious objections which may be brought against 

 this view: i. Calculations seem to show that the amount of crumpling and 

 folding actually found in the mountains is many times greater than could 

 be produced by the contraction of the earth by cooling. But it may be 

 answered (i) that the calculations take no account of the greater coefficient 

 of contraction at high temperatures, and therefore at great depths, (2) and 

 that there may be other causes of contraction besides cooling. For example, 

 loss of constituent gases and vapors from the interior of the earth, through 

 volcanic vents and fissures, has been suggested by O. Fisher (p. 102). 



" 2. Again, it has been shown by Button that it is impossible that the 

 effects of differential contraction should be concentrated along certain lines, 

 so as to give rise to mountain-ranges without a shearing of the crust upon 

 the interior portions, which is inadmissible if the earth be solid. Instead, 

 therefore, of conspicuous mountain-ranges, the effects of differential con- 

 traction would be distributed all over the surface, and be wholly impercep- 

 tible. But in answer to this it may be said that there is no difficulty in the 

 way of shearing, and therefore of such concentration of effects along certain 

 lines, if tJiere be a sub-crust liquid or semi-liquid layer, either universal or 

 else underlying large areas of surface. 



" Still other objections have been raised, but these are so recent that they 

 have not yet been sufficiently sifted by discussion to deserve mention here.' 

 The origin of mountains by lateral pressure is a fact beyond dispute. This is 

 the most important fact for the geologist. How the lateral pressure is pro- 

 duced is a pure physical question which must be left to the physicists to 

 settle among themselves "' (pp. 274-5). 



Leconte treats also of Monoclinal mountains, as found in the 

 Great Basin, which he explains by normal faulting, or vertical move- 

 ment of crust blocks, and finally adds : 



' For a completer discussion of this subject, see " Theories of Mountain 

 Origin," Jour. Gcol, Vol. I., p. 542, 1893. 



