THE 



AMERICAN JOURNAL OF SCIENCE 



[FOURTH SERIES.] 



Art. XYIII. — Abyssal Igneous Injection as a Causal Condi- 

 tion and as an Effect of Mountain-building y by Reginald 

 A. Daly, Ottawa, Canada. 



[Published by permission of the Canadian Commissioner, International 

 Boundary Surveys.] 



Contents. 

 Introduction. 



The shells of compression and tension in the earth. 



The hypothesis of a crust and fluid substratum. 



Purpose of the present paper ; acknowledgments. 

 Thickness of the earth's crust. 



Compression of the substratum ; flotation of the crust. 

 Stresses within the crust. 



Secular accumulation of tension and of cooling cracks. 

 Injection of magma into the shell of tension. 

 Eelief of tensions through abyssal injection. 

 Down- warping of the surface as a result of abyssal injection. 

 The conditions for mountain-building. 



Expansion of the earth's outer shell as a factor in mountain building. 

 Eenewed abyssal injection following mountain-building ; development of 



batholiths. 

 Vuicanism as a result of mountain-building. 

 Summary. 



Postulates. 



Conclusions. 



Introduction. 



The shells of compression and tension in the earth. — 

 Whether the earth, as it cools and contracts, be solid and 

 highly rigid throughout, or whether it consist of a solid crust 

 with an underlying fluid substratum, it is generally held by 

 geologists that there is a "level of no strain" beneath the sur- 

 face. The depth of this level has been computed for a solid 

 earth by Davison and Darwin, who have made various assump- 



Am. Jour. Sci. — Fourth Series, Yol. XXII, No. 129. — September, 1906. 

 14 



