effect of batholithic intrusion 3oo 



Batholith Intrusion as Cause of Folding . 



GENERAL STATEMENT 



The analysis of the theories of mountain-building has shown that each 

 theor}^ has serious drawbacks. The principal of these drawbacks are (1) 

 that the continuity in effects required by the theories is in contrast with 

 the irregular intervals shown by the facts, both in time and in space; 

 (2) the difficulty of securing the amount of horizontal motion which is 

 evident in the folded mountain ranges; (3) the slightness of the initial 

 force appealed to in contrast with the enormous obstacles of friction and 

 cohesion presented by the rocks; (4) the extensive revolving of the crust 

 between the sea and the land required by some theories — a situation 

 which has not taken j)lace since the Paleozoic began. The author's 

 analysis of the theories has led him to the conclusion that another force 

 has operated which is not continuous in time or space and which was not 

 deficient either in initial amount or in horizontal motion. In the search 

 for such a force, which must be a great one, he has been led to consider 

 other phenomena attendant on mountain-building. These are (1) heat, 

 which is evidenced by metamorphism and the growth of new minerals in 

 the deformed rocks; and (2) the force exerted by igneous intrusions. 



The association of igneous intrusions and extrusions with periods of 

 mountain-building has been observed and commented on by many writers, 

 but in all cases known to the author the intrusions have been regarded 

 as results of the mountain-building forces and not as their cause. It 

 seems to the writer, after much consideration, that the case is reversed 

 and that igneous intrusions, which are the greatest examples of heat and 

 force known to us, and which are definitely associated with mountain- 

 building, should be rated as the cause of the building of mountains, 

 which show to us the greatest known results of heat and pressure. In 

 the demonstration of such a relation the same difficulty is encountered 

 by this theory as by others — that is, that the forces and the moving 

 masses acted deep within the crust and must in the main be beyond 

 observation. In most mountain ranges only a few thousand feet of the 

 crust are observable; in the Appalachians, however, parts of the crust 

 have been uplifted so high and worn so deeply by erosion that the ob- 

 server can examine rock masses which originally lay many miles beneath 

 the surface. The conclusions drawn from direct observation in the 

 Appalachians should have special force, therefore, and should be regarded 

 as the best test which we now have of the theories of mountain-building. 



