76 FIELD GEOLOGY. 



are so minute that a pocket-lens must be used in read- 

 ing off the indications. 



The measurements are made along the surface, flat or 

 inclined as the case may be, with a chain 22 yards 

 (= ^- Q of a mile) in length, divided into 100 links. The 

 chain, made with strong wire, has a handle at each end 

 and a brass or other mark every ten links to aid in 

 counting the odd parts of each admeasurement. Ten 

 iron arrows, with pieces of red cloth on each, are carried 

 by the leading chain-man, who puts down one at the 

 end of every chain measured when the extent of ten 

 chains is reached the arrows, picked up in passing by 

 the chain-man at the rear-end, are restored to him, and 

 a note is made of every such ten chains passed over. 



"We must secure the services of three men, or boys, 

 two being required for chaining, and the third for 

 assistance in the taking of our observations. The work 

 can be done with two only, but with a third it is gotten 

 over much more expeditiously of the three men, he 

 who is most to be relied on for care and accuracy, or is 

 accustomed to the work, should be put in the rear of 

 the chain. 



As every spot where the instrument is placed will be 

 constituted a " station," the height from the ground of 

 the objects on which sights are taken should be about 

 the same as that of itself, viz. 5 feet the visual line 

 will then be carried from end to end at a uniform 

 distance of 5 feet from the surface. A light staff of 

 that height, with a cross-piece at top painted white, is a 

 good thing to be carried by the assistant and placed by 

 him on each place in turn where the observations are- 

 taken or without this staff the sight may be taken on 



