818 



DYNAMICAL GEOLOGY. 



fractures of the crust, with friction, and perhaps, also, crushing, along 

 the fractures. The direction of the fractures, according to physical 

 laws, should have been primarily at right angles to the lateral thrust, 

 with sometimes a secondary transverse system. Fractures so pro- 

 duced should also have followed, according to the experiments of 

 Daubree, oblique planes ; and this is the fact with the greater fractures 

 of the crust in mountain-making (p. 803). 



2. Formation of Mountains and Mountain Systems. 



A monogenetic mountain, as has been explained, comprises all the 

 associated elevations that were made in one mountain-making process, 

 and a polygenetic mountain, those of two or more epochs of disturbance 

 combined into a single mountain system. The former may be (1) a 

 single elevation ; or (2) a combination of them making a mountain 

 range; and the latter may be a combination of ranges having in 

 general a similar course, and making a mountain chain or system. 



The following are three ways in which a mountain of one genetic 

 process may have been formed : (1) Through a simple geanticlinal 

 or upward bend of the earth's crust ; (2) through a simple fracture 

 of the crust, and an upward push or shove along the fracture ; (3) 

 through the slow progress of a geosynclinal, and of sedimentary depo- 

 sitions within its area, ending in fracture. The methods by vapors 

 underneath, and by change of temperature, are already remarked upon 

 on pages 814 and 811. 



1. Through a Simple Geanticlinal. 



Geanticlinals or upward flexures in the crust that became permanent 

 elevations in early geological times are rarely to be distinguished. 

 The region of the Cincinnati uplift may be one of them, as explained 

 on page 217. The time of origin was the close of the Lower Silurian. 



Late in geological time, when the crust had thickened much, such 

 movements often resulted in permanent elevations, and many moun- 

 tains of the world — the Rocky Mountains, for example — owe half 

 or more of their elevation above the sea level to geanticlinal move- 

 ments ; but in all such cases, as far as known, the process was subse- 

 quent to other mountain-making action, and perhaps to various epochs 

 of it ; so that the regions that were thus elevated may not be examples 

 of the simple monogenetic kind. 



2. Through a Simple Fracture of the Crust. 



Cases of uplift along great fractures that are not subordinate to 

 other more comprehensive mountain-making work in the region are 

 not often distinguishable. When the plane of such a fracture is 



