SEEPAGE AND DRAINAGE. 445 



artificial channels which the owner of the land has 

 provided. By the natural drainage, creeping slowly 

 by minute quantities down the slope, added to the 

 slow, natural evaporation, two or three weeks, or even 

 a month, are often required to relieve land which 

 might otherwise be dried in a few days. It may be 

 desirable to have the drains covered, in which case the 

 trenches can be half filled with loose materials, such as 

 broken stone, brush, logs, or any debris sufficiently 

 solid to hold up the covering, which should be thick 

 enough to admit of plowing. 



The Steam Irishman. — So pradticable has the 

 plan of open trenches proven that already a number of 

 new canals have been constru(5led which obtain their 

 supply of water wholly from seepage pools or basins. 

 One of these canals is near Platteville, Colorado, and 

 was construdted with a steam dredging-machine floated 

 on a mud-scow, as shown in Fig. 113. This machine 

 is twelve feet wide, and is really a house-boat contain- 

 ing the power for working a dredge or * * steam Irish- 

 man," as it is often called. It cuts a ditch or tunnel 

 through swamps or other low ground, beginning at 

 the head of the proposed canal, and is floated gradu- 

 ally along by the drainage water which follows behind 

 and around the scow. It scoops out dirt, stones, and 

 even small trees at a wonderful rate. Such a machine 

 will do the work of a full gang of men, and can also 

 work in places where men could not possibly operate. 

 By means of these dredges large tradls of land have 

 been drained and made fit for the plow. In some 

 places these canals are cut not only to afford outlet for 

 drainage water, but are utilized for the double pur- 



