TIMBEK-SLIDES, 327 



in sledges, with a lower depot in the valley. Such a slide 

 must be constructed most carefully and strongly, the site 

 for it well chosen, and the gradients very carefully arranged. 

 Temporary slides are used in hringing-down wood from the 

 upper to the lower part of a felling-area, or to a road, and are 

 constructed in a much lighter and less expensive way than 

 permanent slides. They may be made with portable segments 

 (p. 322). 



The construction of slides requires a large quantity of wood, 

 and this is further increased by the slight durability of the 

 latter, for although slides may last longer in damp, shady 

 places, and shorter on sunny aspects, yet they rarely last 

 more than 7 years, and usually repairs are required after 3 or 

 4 years. 



[In the Himalayas, deodar-wood is so saturated with oil, 

 that its heartwood is practically imperishable in mountain 

 districts ; timbers in bridges in Kashmir exposed to alterna- 

 tions of damp and dryness have lasted for hundreds of 

 years, so that very durable timber-slides may be made of 

 deodar. Tr.] 



As progress is made in the construction of roads, slides 

 become less important; at any rate, this applies to slides 

 several miles long, which were formerly so prevalent on the 

 southern declivity of the Alps, where the best constructors of 

 slides are to be found. 



Shorter slides, however, intended to complete communica- 

 tions over steep ground, are still employed extensively in the 

 Alps and other mountain-ranges, and their use is increasing. 



2. Ground-slides. 



Ground -slides are tracks often found on mountain-sides, 

 and are made either on the bare ground by the repeated 

 sliding of logs, or artificially improved in various ways, so as 

 to be fit for sliding. As a rule, a depression on a steep slope 

 is selected, a line for sliding dug along it and pieces of wood 

 placed on it transversely on which the logs may slide, other 

 pieces being placed here and there along the edges of the 

 slide to prevent the logs from leaving it. 



