SECTIONS OF MOUNTAINS. 



241 



without fracture, there will be a complete arch or saddle (fig. 

 361, A). But very often the upper beds are broken through at 

 one or more places in consequence of the violent pressure, and 

 an open arch is produced, forming a fissure- valley (fig. 361, D), 

 the side walls of which rise into ridges (fig. 361, C); but the cor- 



Fig. 362. 



Fig. 363. 



Fig. 364. 



Fig. 365, 



Sections of Mountains. 



Fig. 361. A. Complete arch. B. Basin-valley. CC. Ridges. D. Open 

 arch, fissure-valley. I. Primitive rocks. II. Carboniferous. III. 

 Trias. IV. Jurassic. V. Cretaceous. VI. Tertiary. 



Fig. 362. Denuded arch. I. Trias (arch). II. Lias (Liassic Combe- 

 valley). III. Brown Jura (ridge). IV. Lower White Jura (Ox- 

 fordian Combe- valley). V. Upper White Jura (chain of the third 

 order). 



Fig. 363. Chain of a single series. 



Fig. 364. Chain of two ridges. 



Fig. 365. Chain with margins turned over. 



respondence of the strata, although broken, will still be clearly 

 shown. This fissure-valley is afterwards often enlarged by 

 erosion and by dislocations ; and the removal of the superior 

 beds by these means may bring to light the unbroken inferior 

 beds belonging to the same arch (fig. 362, 1.). When the arch 

 VOL. n. R 



