DRY-LAND DREDGING 251 



or left to be washed away by the action of the water, extra material 

 being taken out so as to bring the bottom back to grade. 



The straddle ditching machine is built by Mayer Brothers, Inc., 

 of Mankato, Minn. It is mounted on two steel beams that straddle 

 the ditch to be excavated. The four ends of these beams are provided 

 with a two-wheel oscillating truck, which runs on plank ways, 6 in. 

 thick and 3 ft. wide, built in 20 ft. sections. These plank ways 

 are moved forward by two special cranes provided on the dredge 

 for that purpose. The whole machine is moved ahead by means 

 of a cable run to a deadman in front, without interfering with the 

 work of the dredge. In other respects the straddle ditching machine 

 is like a dipper dredge. 



A number of steam-shovel manufacturers make some types or 

 type of ditching machine to be mounted on a scow for working 

 either for dry-land excavation or when there is water. These all 

 have dippers and we need not comment on them further. 



It is but natural that most dry-land excavation is done by other 

 means than dredges, but dredges are being used more and more 

 for such work, as it is found to be economical, especially when 

 large quantities are to be moved. Another method of dry-land 

 excavation is by means of a jet of water. This is known as hydraulic 

 sluicing and is done by means of a nozzle, known as a monitor or 

 giant. This method is used also for mining, and earth is loosened 

 and in some cases elevated by means of hydraulic elevators, which 

 are described elsewhere. 



The Chicago Drainage Canal, built during the nineties, was a 

 case of dry-land excavation, upon which many different classes of 

 machines were used, including dredges, steam shovels and cable- 

 ways. A large number of special machines were also designed for 

 this work, and when grapple buckets were used on them, they 

 could be classed with dredges, but the majority of such machines 

 were designed to dispose of the spoil and not to excavate it. 



The rebuilding of the Erie Canal hi New York State into a 1000- 

 ton barge canal, is also another example of dry-land excavation 

 that has brought out special machines, and a number of large dredges 

 for carrying on the excavation. Power scrapers are being used 

 both with movable derricks, derrick cars and cableways, and grapple 

 buckets have been operated by means of a large steel overhead 

 bridge near Rochester, N. Y. 



The Panama Canal is the greatest undertaking that the world 



