PUDDLING. 219 



expense may bo greater, because of the more perfect con- 

 solidation of the work by the trampling of the horses, 

 and the cutting of the wheels. It should be disposed in 

 regular layers, of 2 to 3 feet in thickness, over the whole 

 work. These layers should be depressed at the center of 

 the work, so as to give a basin shaped form to the section. 

 This is shown in fig. 101, in which the puddle wall is 

 placed in the center of the dam. 



The puddle work should increase in thickness downward, 

 2 inches for every foot of hight over and above the proper 

 thickness at the top water line of the dam. The object of 

 the puddling is only to give security against any imper- 

 fection in the rest of the work, through which water 

 might percolate ; but if the earth work is properly con- 

 structed, of the best materials, it is probable that the 

 water would never penetrate more than a few feet beyond 

 the surface, and would never reach the puddled portion. 

 Nevertheless, puddling should not be omitted, unless 

 under the most favorable circumstances, and even then 

 in no case in which disaster or loss of life might result 

 from a failure, as when a large body of water is impound- 

 ed in a reservoir. When a sufficient quantity of selected 

 materials has been placed in the dam, the facing on either 

 side may be continued to the proper slope, with any 

 material that will serve the purpose ; the inner slope may 

 be finished with soft material, such as peat, or dredging 

 from marshes, when no disturbance by waves, or washing 

 is to be apprehended, but the outer slope should consist 

 of solid matter, which will retain its position, and will 

 not crumble, as for instance, broken stone, rock, or 

 shaly soil. 



When an earth dam is thrown across a stream, the most 

 important points to secure are, the waste gates, the outer 

 slope over which surplus water flows, and the foundation. 

 The waste gates should be built in one of the banks, 

 which should be dug away for this purpose, and the 



