'0 FIELD GEOLOGY. 



staff on along the road, which runs about in the right 

 direction, to a distance roughly equal to that of the 

 instrument from the milestone. A reading is taken 

 upon it (210), entered as a "fore-sight," checked by a 

 second reading, and the level carried forward some chains 

 beyond the staff when all the operations are repeated. 

 The staff will then be turned round to face the instru- 

 ment in its new position, but care must be taken that 

 the back- and fore-sights are read off without other 

 alteration in its position. 



The levelling is thus carried on by the road, just off 

 the real line, to the cross- ways, when it must be managed 

 for the staff to be placed on the road where it is cut by 

 the section line, this being one of the points to be scaled 

 from the map. Then the line is followed, or nearly so, 

 in the direction of the cottages by which it passes, down 

 the escarpment (where shorter sights will be necessary 

 owing to the rapid fall), by the well, across the brook, 

 past the church, and ends by the stream on the W. side 

 of the map. 



