ESTIMATES AND CAUSES OF CRUSTAL SHORTENING 53 



occurs this is a further cause for crustal corrugation. Thus the 

 transfers of magma are both effect and cause of crustal corruga- 

 tions. 



So far as I know, Lyell 1 was the first to suggest that there 

 is a connection between folding and igneous intrusions. How- 

 ever, Fisher 2 went further than Lyell, and urged that vulcanism 

 is the chief cause of crustal corrugation. His argument may be 

 very briefly summarized as follows: Fissures form "through 

 metamorphic changes. When these fissures originated below 

 and v are propagated upward, they become filled with elastic vapor, 

 and compression results." According to Fisher, it is the expan- 

 sive force of the vapor which makes the openings, and consequent 

 corrugations, and these openings are occupied by the magma. 

 So far as my present purposes are concerned it makes no differ- 

 ence how the intrusives found places for themselves. I merely 

 insist upon the fact that somehow great spaces formerly occupied 

 by solid rocks came to be occupied by the magma. 



Shaler 3 has also appealed to igneous intrusions as a cause 

 for mountain-making, and in a manner similar to Fisher. He 

 thinks that in many places of New England the dikes occupy 

 from one-twentieth to one-tenth of the superficial area. 



However, neither Fisher nor Shaler consider the shrinkage of 

 the nucleus of the earth due to the loss of the magma for both 

 intruded and extruded materials, or the crustal corrugation which 

 must result from this transfer of material. 



In closing this part of the subject, it should be noted that 

 crustal corrugation caused by transfers of magma involves no 

 contraction of the earth nor lessening of its surface as a whole, 

 except as magmatic transfer results in loss of heat by convection, 

 as explained (p. 43). It may also be remarked that the earth 

 contraction due to loss of heat caused by actual transfers of 



'Principles of geology, by Charles Lyell: 10th ed., London, 1867, Vol. I, pp. 



134-135- 



2 Physics of the earth's crust, by Osmond Fisher: London, 1881, pp. 185-207, 



and pp. 284-286. 



3 The crinetic hypothesis and mountain-building, by N. S. Shaler : Science, 

 Vol. XI, 1888, pp. 280-281. 



