266 A. Vaughan — Corrugation of the Earth's Surface. 



It would seem that there could be uo difficulty in assuming 

 sufficient separation space in all known rocks to allow of this 

 extent of approximation. But the case is in reality much stronger 

 than appears in the above figures, for we have assumed no con- 

 traction to go on in any of the overlying rocks, whereas contraction 

 must be in progress in all those rocks whose constant temperature 

 exceeds the mean average surface temperature, and this at a faster 

 rate than in the underlying interior, with the result that the 

 separation spaces throughout the overlying shells are being increased 

 so as to allow of additional approximation. 



There would seem, then, no difficulty in accepting the idea that 

 the crust will in general follow the contracting interior and not 

 be thrown into folds, but will accommodate itself to a smaller area 

 by the closer approximation of its component parts. 



More space has been spent in considering this point than would 

 perhaps seem necessary ; but the theory has very generally been 

 accepted that corrugations are caused by the shrinking away of a 

 contracting nucleus from a consolidated non-contracting crust.^ 



It will be well, consequently, to examine what amount of corru- 

 gation could be produced on the supposition that the crust is 

 non-contracting and incapable of accommodating itself to a smaller 

 area. The interior is imagined to shrink away, but, by the action 

 of gravity, the heavier areas of the heterogeneous crust are retained 

 in contact with the shrinking nucleus. It follows, on the hypothesis 

 of an incompressible crust, that the intermediate portions will be 

 thrown into folds. 



Employing the same data as before, and further assuming that the 

 two areas, which, owing to the effects of gravity, sink with the con- 

 tracting nucleus, are 1000 miles apart, we find by an easy calculation 

 that the greatest possible height to which the under surface of the 

 intermediate portions of the crust could rise is less than 5000 feet. 



This is on the assumption that the crust is bent into two planes 

 meeting above the middle point of the contracting arc. Again, since 

 we cannot suppose the contracting nucleus to lie many miles beneath 

 the surface, this maximum elevation will not be sensibly increased 

 at the surface itself. It is very important to point out the favourable 

 exaggeration involved in the data employed in the above calculation. 



In the first place, owing to resistance from within, no shell could 

 contract to its full extent; secondly, a fall of 10° would represent 

 an enormous loss of heat in the interior ; again, it is improbable 

 that the two areas which sink with the nucleus could be so far 

 apart ; and lastly, that the crust should be thrown into the form 

 supposed is utterly impossible, and at variance with the structure 

 of all known mountain systems. 



One further point in regard to this theory : — 



Since the eff"ect of the shrinking interior must be to draw closer 

 together those portions of the crust which are in contact with it, 

 the force between any two portions of the earth's crust must be one 



1 A discussion of the later theory of Mr. Mallard Eeade is contained in Part II. 

 of this paper. 



