482 TIMBER BONDS 



Hypsometer. See height measure. 



Ice a Road. To sprinkle water on a logging road so 

 that a coating of ice may form, thus facilitating the 

 hauling of logs. 



Ice Guards. Heavy timbers fastened fan shaped about 

 a cluster of boom piles at an angle of approximately 

 thirty degrees to the surface of the water. They pre- 

 vent the destruction of the boom by ice, through forc- 

 ing it to mount the guards and be broken up. 



Increment. The volume or value of wood produced dur- 

 ing a given period by the growth of a tree or of a 

 stand. Three kinds of increment are distinguished: 

 Volume increment is the increase in volume of a tree 

 or stand; quality increment is the increase in value 

 per unit of volume; price increment is the increase re- 

 sulting from an advance in the price of forest products 

 independent of quality increment. 



Index. The highest average actually found upon a given 

 locality. The term index applied to stand, diameter 

 growth, height growth, increment and present and fu- 

 ture yield is the equivalent of normal, when normal 

 is used to describe the assumed standard based upon 

 actual measurement. 



Index Forest. That forest which in density, volume and 

 increment reaches the highest average which has been 

 found upon a given locality. Measurements of such 

 a forest provide a standard for comparison with other 

 forests of the same age and composition, grown under 

 similar conditions. 



Intermediate. Having the crown shaded on the sides, 

 but free to light on the top. 



Intermediate Yield. All material from thinnings or 

 from any cuttings not intended to invite or assist re- 

 production. See yield. 



Intolerant. Incapable of enduring heavy shade. 



Irregular Forest. Forests in which the trees differ con- 

 siderably in age. 



Jack Chain. An endless spiked chain, which moves 

 logs from one point to another, usually from the mill 

 pond into the sawmill. See bull chain. 



Jack Ladder. See gangway. 



Jackpot. 1. A contemptuous expression applied to an 

 unskillful piece of work in logging. 2. An irregular 

 pile of logs. 



Jam. A stoppage or congestion of logs in a stream, 

 due to an obstruction or to low water. 



Jam Cracker. See head driver. 



Jammer. An improved form of gin, mounted on a mov- 



