INTRODUCTION 97 



ment and mutual friction of material under traffic. Water action 

 is partly mechanical, allowing more ready movement of ill-con- 

 solidated material. It is partly chemical, removing any con- 

 stituents of the stone or its binding material which are soluble or 

 capable of decomposition. Frost action and that due to traffic 

 are entirely mechanical. Transport is almost entirely mechanical, 

 and is effected by wind or water, the disintegrated matter being 

 swept off and eventually deposited elsewhere. That removed 

 must be replaced by periodical surfacing if the road is to be 

 maintained in usable condition, for the condition of the removed 

 material when it comes to be deposited by wind or water is not 

 suitable for further road making or mending, although some 

 misguided surveyors save it up carefully and eventually use 

 it as a cheap and very bad binding material. 



The faster the surface disintegrates the more rapidly is the 

 material carried away. On the other hand, the removal of mud 

 and dust by torrential action continually exposes new surfaces to 

 disintegration. The checking of either process lengthens the life 

 of the road, and the ideal road would be one in which there was no 

 wind or water action and the wear and tear restricted to that 

 due to the traffic itself, and one built of such hard material that 

 even this wear was reduced to a minimum. Towards this end 

 waterproofing is an important step, because it reduces disinte- 

 gration very considerably. Lessening the camber and gradient 

 checks the speed and hence the transporting power of running 

 water, and the construction of immovable, well-drained, founda- 

 tions diminishes the breaking up of the surface by the weighty 

 traffic. Further improvements will come in the direction of 

 lessened watering, avoidance of any hammering or plucking action 

 on the road, and the interposition of softer and more resilient 

 substances between the traffic and the road. 



The examples thus described serve very well to introduce the 

 subject of natural denudation. It is only necessary to replace the 

 surface of a road by that of a landscape, and the same or similar 

 agencies will be found at work. These should naturally be studied 

 next, attention being devoted to such parts of the process as the 

 district allows to be seen in operation. 



VOL. vi. 7 



