CHAPTER II. 



STRATIFIED ROCKS. 



SECTION I. THEIR STRUCTURE AKD POSITION. 



LET any one examine the rocks of a quarry of limestone 

 or sandstone, and he will find that the stone lies in regu- 

 lar beds. In some places these beds will lie level (Fig. 

 91), in other places they may be inclined (Fig. 92). For 

 example, throughout the valley of the Mississippi they 

 are usually level, while in mountain-regions they are 

 usually inclined. The next most conspicuous structure 

 will probably be the cross-divisions called joints., by 

 which the beds are 

 broken into separ- 

 able blocks. These 

 are found in all 

 rocks, are not char- 

 acteristic of strati- 

 fied rocks, and 

 therefore we say 

 nothing more about 

 them now. On ex- 

 amining a little 

 more closely, the 

 beds will be seen to 

 be subdivided by 

 faint lines similiar to those observed in a section of sedi- 

 ments, and known to be produced by the sorting power 



179 



S8 



8/1 



FIGS. 91, 92. Sections of horizontal and inclined 

 strata : s, soil ; ss, sandstone ; sh, shale ; Ls t 

 limestone. 



