474 APPENDIX B 



gallery. Their dimensions depend on size of galleries. Diameters vary from 5| 

 to 24 inches. Square props are used for similar purposes. Small round props used 

 principally in coal mines are termed mine props and rim from 4 inches up in diam- 

 eter and from 4 to 10 feet in length. These timbers are used to support the ground 

 and must be straight, sound and free from knots that will impair the strength of 

 the piece, or from defects affecting strength or durability. 



Mine timber is bought by the linear foot, by classes based on top diameter. 

 Spht props mast have a cross-sectional area in square inches equal to that of a round 

 post of minimum .specified diameter. 



Pole lagging varies from H to 5 inches in diameter at small end and averages 16 

 feet in length. Four- to five-inch poles may be split. Lodgepole pine is the 

 principal .species used. Lagging is bought by the piece. 



Mine Ties. Cross ties for mine tramways are usually 5 to 5^ feet long but may 

 be from 3 feet to 6 feet in length, and var>' for individual mines, from 3 by 4 inches 

 to 5 by 6 inches in diameter. Their small size makes a market for very small timber, 

 which can be grown in 20 to 30 years. Ties are bought by count, and on basis of 

 specifications. 



Round mine timber of these classes and mine ties not only utilize the entire stick, 

 but permit the almost complete utilization of the felled tree and of the stand. In 

 fact, the tendency is to exploit young second-growth stands while still too small to 

 bear seed, and under private management forests in mining regions are rapidly 

 destroyed. The same conditions permit of thinnings in dense stands, the removal 

 of small diseased trees and a short rotation, and under forest management offer 

 verj- favorable conditions for profitable j^roduction of timber. 



369. Cross Ties. Standard railroad cross ties are either hewn, with two jiarallel 

 faces, or sawed to specified dimensions. Switch ties are sawed in sets of graduated 

 lengths. Hewn ties, termed also pole ties, are made from round bolts hewn on two 

 sides to produce parallel faces. Bolts 14 inches and over in diameter are usually 

 split into two or more ties, hewn on four sides. Hewn ties are preferred to sawed 

 ties as they are said to be more durable. 



The standard specifications for cross ties of the U. S. Railroad Administration 

 have since March, 1920, been adopted with slight changes by over two-thirds of the 

 railroad mileage of the country. These specifications are shown graphically in Fig. 

 88. The specifications of the Penn.sylvania Railroad System, based on the above, 

 are as follows: 



All ties shall be free from any defects that may impair tKeir strength or thiraljiUty 

 as cross ties, such as decay,' splits, shakes, large or numerous holes - or knots,' or 

 oblique fiber with slope greater than one in fifteen. 



Ties from needle-leaved trees shall be of compact wood with not less than one- 



' Ties must be rejected when decayed in the slightest degree, except that the 

 following may be allowed: in cedar, " pipe or stump rot " up to 1§ inches diameter 

 and 15 inches deep; in cypress, " peck " up to the limitations as to holes; and, in 

 pine, " blue sap stain." 



2 A large hole in woods other than cedar is one more than ^ inch in diameter and 

 3 inches deep within, or one more than 1 inch in diameter and 3 inches deep outside 

 the sections of the tie between 20 and 40 inches from its middle. Numerous holes 

 are any number equaling a large hole in damaging effect. 



' A large knot is one exceeding in width more than \ of the width of the surface 

 on which it appears; but such a knot may be allowed if it occurs outside the .sections 

 of the tie between 20 and 40 inches from its middle. Numerous knots are any 

 number equaling a large knot in damaging effect. 



