400 WATER-TRANSPORT. 



straiul the timber, deep culverts with sluice-n;ates may be made 

 and opened to pass the water under the boom. 



(c) Further Details regarding Booms. — In the preceding para- 

 praplis, a distinction has been made between lateral or terminal 

 booms, but the latter may be of several kinds. Every boom, 

 whatever its dimensions, which catches floating wood at a 

 timber-depot is a principal boom. Owing to certain conditions 

 of a locality and want of sufficient room, it is not always possible 

 to supply evei-y river timber-depot with a principal boom ; or the 

 risk cannot be incurred, in the case of numbers of saw-mills 

 situated along a stream, of entrusting the supply of the 

 thousands of logs they require for their annual work to one 

 lioom only, which is always liable to be broken. In such cases, 

 subsidiary booms are used in order to ensure a supply of wood 

 for all the saw-mills. 



For this purpose narrow parts of the stream are selected, 

 confined on either side by ro-^ks, and booms are here erected with 

 moveable gratings, from which the wood can be again despatched 

 down-stream in small sweeps to the different saw-mills or timber 

 depots. 



Not unfrequeutly a stream is broken-up by booms at not very 

 long intervals ; this is generally for charcoal-burning, in order to 

 land the wood required where permanent charcoal-kilns are main- 

 tained ; or each forest owner or principal wood-merchant has his 

 own boom, in order to collect his own wood and float it separately 

 from that of other owners to the principal boom ; or the saw- 

 mills situated along the stream have each its special boom, 

 provided with passages to allow extraneous wood to pass through 

 them. 



Subsidiary booms are sometimes erected in strong streams 

 below the principal boom, where, owing to occasional floods, 

 there may be danger of the latter breaking. Wherever floating 

 timber is rafted, or passed in lines of logs across a lake, most of 

 the water-logged wood would enter the lake and sink to the 

 bottom without possibility of recovery, were not a boom stationed 

 at the point where the stream used for floating passes into 

 the lake. 



