ORIGIN OF MO UNTAIN RANGES. $ 6 1 



after the mountain formation ceases. In these, however, mate- 

 rials are ejected not by mountain-making forces, but by the elastic 

 force of vapor from percolating waters. All these eruptive 

 phenomena are, therefore, associated with mountain ranges. 



2. Faults. — In folding, and especially overfolding, the strata 

 are, of course, often broken and the upper wall of the fissure is 

 pushed over the lower wall by horizontal thrust often thousands 

 of feet, forming reverse faults and so-called thrust planes. Hence 

 this style of faults are everywhere associated with strongly folded 

 rocks, and, therefore, with mountains, and are indisputable evi- 

 dence of horizontal crushing. In other places than mountains, 

 and in horizontal or gently folded rocks, the other style of faults, 

 i. e., normal faults, are more common. 



3. Mineral Veins. — The filling of fissures at the moment of 

 formation with fused matter constitute dikes ; but if not so filled, 

 they are afterwards filled by a slow process of deposit from cir- 

 culating waters and then they form mineral veins. These, there- 

 fore, are also common in mountains. 



4. Earthquakes. — Again, the immense dislocations of strata 

 which we find in faults did not occur all at once, but slowly 

 through great lapse of time ; and yet on the other hand not by 

 uniform slipping, but by jerks, a little at a time. Every such 

 readjustment of the walls of a fissure, whether by increasing 

 lateral pressure (reverse faults) or by gravity (normal faults), 

 gives rise to an earthquake. Earthquakes, therefore, although 

 not confined to, are most common in mountain regions, espe- 

 cially if the mountains are still growing. 



Thus, leaving out the monoclinal type which seems to belong 

 to different. category, all the phenomena, major and minor, of 

 structure and of occurrences connected with mountains, are 

 well explained by the theory of lateral pressure acting on lines of 

 thick sediments accumulated on marginal sea-bottoms and 

 softened by invasion of interior heat. This view is therefore 

 satisfactory as far as it goes, and brings order out of the chaos of 

 mountain phenomena. It has successfully directed geological 

 investigation in the past and will continue to do so in the future. 



