THE PROSPECTOR'S HANDBOOK. 



are bent into ridges or troughs for considerable lengths they 

 are called respectively anticlinal and synclinal (Figs. 8, 9). 



When one series of strata is parallel to another, the two 

 are said to be conformable ; when not parallel, unconform- 

 able, as in Fig. 10. 



In this illustration the one set of strata (dipping r> ) 



Fio. 10. 



has been tilted up from its original horizontal position ; 

 after which the horizontal strata were deposited. 



The wearing away of rocks may be produced by various 

 denuding agents, such as wind, rain, running water, sea, 

 frozen water, &c. Sometimes the water acts chemically and 



FIG. 11. GBAPTOLITES. 



FIG. 12. TRILOBITK. 



rots the rock, while rivers and rain dig and saw, the sea 

 planes, the expansion of ice splits, and glaciers file it. As 

 to weathering well, the sandstones seem to be less liable to 

 disintegration than most rocks, unless they contain iron or 

 carbonate of lime ; limestones are readily attacked by water. 

 While some rocks can be split along the layers as origi- 

 nally deposited, other fine-grained ones, such as slate, can 

 be most easily so in a direction across the line of bedding. 

 In contorted strata the lines of cleavage are parallel, as in 

 Fig- 15. Cleavage is probably due to lateral pressure. 



