CONSTRUCTION OF THE EARTH. 133 



representation of such an upheaval. Fissures of various 

 dimensions, sometimes of immense size, are made in this 

 way, and this is the origin of many of the valleys which 

 we see with steep, bold sides. Chasms and caverns are 

 produced by such upheavals ; water, by its erosive agen- 

 cy, acting, however, at the same time, and afterward in 

 many cases, especially where there are caverns of consid- 

 erable extent. Natural bridges are the result of up- 

 heavals, an example of which is given in Fig. 56, repre- 

 senting that of Icononzo, in South America. 



Fig. 56. 



217. Strata at different Angles. One consequence of 

 upheavals with fracture is that we have strata lying at 

 different angles, as is often shown when their projecting 

 ends or sides are laid bare. The order of the rocks is 

 thus brought to view sometimes to a great extent, as in 

 the case of Snake Mountain, in Vermont, represented in 

 Fig. 57 (p. 134). The place of fracture is at c, and there 

 is brown clay at e, extending from here west six miles to 

 Lake Champlain, and lying upon w, limestone rock. I 

 will trace the layers of rock up the mountain. At b we 



