The Lithosphere 



of plant debris probably, for the most part, in swampy 

 regions. 



It is a character of most sedimentary rocks that they 

 still retain evidence of their accumulation layer upon 

 layer. This is most marked when successive beds 

 consist of different material, but even thick deposits of 

 homogeneous materials give evidence of their sedi- 

 mentary origin by the presence of planes, known as 

 planes of bedding or stratification planes, along which 

 they may be separated into sheets or slabs, and which 

 appear on cliffs and quarry faces as parallel cracks. 



In their original position these bedding planes are 

 sensibly horizontal, but very frequently, especially 

 amongst the older rocks of the Earth's crust, they are 

 highly inclined, or in some instances actually vertical. 



As we cannot imagine the accumulation of such 

 sediments in highly inclined or vertical layers, we are 

 driven to the conclusion that the rocks have been dis- 

 turbed after their consolidation, and that the layers have 

 acquired their inclination as a result of movements of 

 the land, a view which is confirmed by the occurrence 

 of strata which have been folded into curves, or even 

 crumpled into zigzag forms, which are often of a most 

 complicated nature. 



The inclination of a bed of rock to the horizon is 

 spoken of amongst geologists as its "dip," and is usually 

 expressed in degrees, while the direction of the dip is 

 described with reference to the points of the compass. 

 Thus a seam of coal, or other bed, might dip towards 

 the south at an angle of 10, and in that case, if exposed 

 in a cutting running in an east and west direction, i.e. 

 at right angles to the dip, the seam would appear to 



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