HOBIZONTAL SECTIONS. 



The levelling is carried on in the same manner over 

 the chalk outlier, care "being taken to obtain the heights 

 at, or as nearly as possible upon, the geological boundaries. 



It will be seen from the above example of a level- 

 book that the heights of certain definite stations only 

 are worked out those of the others being unnecessary, 

 and probably off the line. The method of procedure is, 

 to add up the " rises " and " falls," to subtract the smaller 

 sum from the larger the remainder to be added to or 

 deducted from the height of the last, station where it 

 was calculated, according to the predominance of " rise" 

 or " fall," as the case may be. In making the additions, 

 all " intermediate " sights are to be disregarded, the cal- 

 culations at those places being enclosed between two 

 lines to indicate that they are not to -be included. The 

 final result may be checked by adding together all the 

 " back- and fore-sights," deducting the one amount from 

 the other, and the result from, or adding it to, the last 

 height obtained. 



