ORIGIN OF MOUNTAINS. 



801 



2. Fractures, Faults, Joints. 



1. Fractures, Faults. — The production of fractures through change 

 of temperature, and, especially, cooling, has been briefly treated on 

 page 720. The results of lateral pressure have been experimentally 

 illustrated by Daubree. In one of his experiments he used an oblong 

 square prism consisting of layers of beeswax, and applied the force at 

 the middle of the two ends, after protecting them by small blocks or 



Fig. 1153. 



Prism of layers of wax of different colors, (x %.) 



plates of the same cross-section. Fig 1153 represents, half the nat- 

 ural size, the prism ready for the experiment. One of the results, 



Fig. 1154. 



Fig. 1155. 



Fig. 1156 



after applying the pressure, is shown 

 in Fig. 1154; and another, after 

 using a stronger pressure, in Fig. 1155. 



In both a flexure becomes the course of a fracture and also of a 

 fault. In Fig. 1156 are shown two oblique fractures and faults, ob- 

 tained in another trial. The frac- 

 tures have their planes parallel as 

 well as oblique ; and the faults were 

 made by a shove up along the ob- 

 lique surface. So the greater frac- 

 tures of mountain regions often have 

 the obliquity (p. 793) as well as par- 

 allelism, and sometimes have been 

 faulted in the same way, though in minor faults the displacements 

 have generally been made by a dropping of the opposite side. The 

 direction of dip of the plane of fracture, as the figures show, is in the 

 case of a synclinal bend the reverse of that in the anticlinal. 



In subjecting to vertical pressure a square block of wax, having a 

 breadth of five and a half inches and a height of about a foot, an ob- 

 lique diagonal fracture was made with some bulging of the sides ; and, 

 51 



