574 DEPARTMENT OF THE INTERIOR 



2 GEORGE V., A. 1912 



tion due to the play of other cosmical forces or of forces induced by the hetero- 

 geneity of the crust, may similarly cause dislocation in the shell of tension. 

 The conclusions may be similarly summarized: — 



1. The abyssal injection involves condensation of the matter in the shell 

 of tension. Cracks are closed and much of the accumulated tension is relieved 

 by an enforced creep of matter away from the injected body. So long as the 

 body remains fluid the stretching of this shell due to continued cooling of the 

 earth is accomplished by creep of matter in the same directions. The amount 

 of creep is at a maximum above the zone of injection and decreases to a 

 minimum at certain distances to right and left of the middle line of the zone. 



2. This lateral creep induces a down-warp of the earth's surface imme- 

 diately overlying the zone of condensation. The resulting geosynclinal may 

 be the seat of prolonged sedimentation. If so, the weight of the sediment itself 

 tends to increase the lateral creep in the shell of tension and the down-warp 

 slowly deepens. 



3. The shell of compression is already weakened at the angles of down- 

 warp; it is further weakened by the sedimentary blanket which, comparatively 

 little resistant itself, causes a softening of its basement through a rising of the 

 isogeotherms.* When the filling of the geosynclinal has sufficiently thickened, 

 the shell of compression, owing to its secular accumulation of stresses (which 

 are intensified by metasomatic changes in the shell), begins to collapse. Moun- 

 tainous forms and structures result. 



4. The complete shearing apart of the shells of compression and tension 

 during the orogenic revolution releases the tensions still unrelieved in the 

 underlying shell. Abyssal injection on a large scale is thus initiated or con- 

 tinued in the shell of tension. The relief of compressive stresses in the act 

 of building the mountains first occasions the possibility of magmatic stoping and 

 thus of the extensive assimilation of gneisses, schists, and sediments by the 

 primary, basaltic magma. The differentiation of the compound magmas of 

 assimilation may explain the batholithic central granites of mountain ranges, 

 along with their satellitic stocks, injected bodies, and volcanic outflows. 



5. The regional warpings of the earth's crust may be partly at least referred 

 to the varying strengths of abyssal injections from a fluid substratum. 



6. The location and alignment of mountain ranges, the location and 

 elongation of geosynclinals, the final development of igneous batholiths and 

 satellitic injections, are all interdependent and related to special zones of 

 powerful abyssal injections from the substratum. These zones are, in the large, 

 located by cosmical stresses affecting the earth along special azimuthal lines. 



7. Mountain building causes relief of compressive stresses in the superfi- 

 cial shell. The surface outflow of magma, either secondary or directly derived 

 from the substratum, may therefore be specially pronounced after an orogenic 

 revolution. In general, the theory of vulcanism is also fundamentally affected 

 by the doctrine of the shell of tensions which are not entirely relieved by the 

 compressive extension of that shell. 



*Perhaps much of the heat thus locally conducted is of radioactive origin. 



