210 



FIELD GEOLOGY. 



section crossed the fault at any other point, by ascertain- 

 ing the depth beneath the surface, at such point, of each 

 part of the broken coal-seam, or each part of the under 

 surface of the sandstone calculated from its boundary. 



The dip of the beds 

 in the section, fig. 22, 

 is shown much less 

 than it would be if the 

 line of section coincided 

 with that of the dip; 

 in this case it deviates 

 therefrom as much as 

 45 degrees. The varia- 

 tion and the method of 

 determination of the dif- 

 ference are explained in 

 Part II. In this example 

 the dip of the limestone 

 at its boundary is about 

 10 30', judging from that 

 ^ observed in the quarries 

 on either side. By dia- 

 gram the apparent angle, 

 corresponding to 10 30', 

 with 45 deviation, is- 

 7 30' only, as drawn on 

 the section; where the 

 line of section first 

 crosses the boundary of 

 the sand the dip is 



8 30', and this angle 

 with the same variation shows 6 only, as represented. 



