18 BULLETIN 300, U. S. DEPARTMENT . OF AGRICULTURE. 
Owing to its long reach, the grab-bucket dredge is often used for 
levee construction. It, however, is not very extensively used for 
the excavation of drainage channels, although there are certain con- 
ditions under which it can be used to greater advantage than can 
the dipper dredge. It excels in handling the muck found on the 
prairie lands of southern Louisiana and in certain other localities, 
and under such conditions is better adapted to ditch and levee con- 
struction than is the dipper type. The latter, however, is preferable 
for digging hard soil and stumps. 
THE DRAG-LINE SCRAPER EXCAVATOR. 
The drag-line scraper excavator is a type of dry-land machine that 
has come into prominence only within the last few years. It has 
made feasible the cheap construction of much larger ditches and 
levees than is possible by the use of any other type of machine. 
In the type most commonly used, the engine platform, engine 
house, and boom are connected and revolve on a turntable which 
is secured to a lower platform built up of structural steel sections. 
This is known as the revolving or rotary type and is illustrated in 
Plate II. Upon the upper surface of the lower platform is riveted 
the track upon which the swinging circle revolves, and in its center 
is the pivot bearing. The turntable is a steel-frame circle supported 
by several wheels which rest upon the track. The upper platform, 
which is also built up of standard steel sections, is held to the lower 
platform by means of a central pivot. 
In the stationary type the engine platform is fixed; the boom is 
pivoted at its lower end and is the only part of the machine which 
swings. This type is illustrated in Plate IV, figure 2. 
The power equipment of the drag-line excavator may be either 
steam, gasoline, or electric. Unlike the floating dipper dredge, the 
internal combustion engine has been used with success on drag-line 
excavators and meets with favor among contractors. For the steam 
plant the boiler most commonly used is either the locomotive or the 
Scotch marine return-flue type. On the smaller machines vertical 
boilers are sometimes employed. The engines used consist of two 
sets, the main engines and the swinging engines. The former are 
set in front and are of the horizontal double-cylinder type, with 
engines and drums self-contained on a single cast-iron or steel bed 
plate. 
Sometimes the swinging is done by a mechanism attached to the 
main engine. Ordinarily, however, separate swinging engines are 
provided. In the rotary type these engines drive, through a series 
of gears, a pinion which engages the circular rack on the lower frame. 
Where electricity can be secured cheaply the machines can be operated 
very economically by this power. 
