328 WOOD TRANSPORT BY LAND. 



In the Black Forest wet sloping meadows are used for this 

 purpose, the line of the slide being bounded by logs. In the 

 Alps the method of sliding along the ground often alternates 

 with timber-chutes. Ground-slides are used for the transport 

 of logs only. 



A ground-slide serves its purpose only when its base and 

 walls are sufficiently firm and smooth ; therefore all stones, 

 roots, etc., must be removed, intervening rocks blasted, the way 

 improved here and there by laying down transverse pieces of 

 wood, while in the more difficult places which have to be 

 traversed short wooden slides are constructed to complete the 

 work. 



It is evident that ground-slides cannot be maintained in 

 workable condition for any prolonged length of time. If they 

 have no rocky subsoil they are torn-up soon by drainage water, 

 and may become buried in silt, gravel, and other debris. 



Sometimes a wire rope is fastened to the logs whilst they 

 descend a ground-slide. A rope is coiled round a windlass at 

 the top of the slide so that as a log goes down attached to one 

 end of the rope, the other end is wound round the windlass 

 ready to be fixed to another log as soon as the former has 

 reached its destination ; often three or more logs are fastened 

 one behind the other, and go down together. The windlass 

 works with a simple brake arrangement. The logs may be 

 placed in trucks and these let down a tramway by the rope. 



Although ground-slides should possess steep gradients, yet 

 if they are used when covered with snow or frozen, the 

 gradient need not exceed 20 to 25 per cent., especially when 

 they are well constructed and bounded by logs placed laterally, 

 for in such cases descending logs soon attain a very high 

 velocity. 



3. 



In some valleys leading from the Black Forest, especially 

 those of the Wolf and Kinzig, regularly constructed roadways 

 are used for sliding logs and sledging, as shown in Fig. 204. 



It has been laid down already on p. 308 that roads when 

 used as slides should have gradients of 9 to 18 per cent., and 

 more, and should be steepest above and become gradually level 





