124 Modern Fishculture in Fresh and Salt Water. 



screen should be at the least calculation nineteen inches 

 each way, giving 361 square inches, which will allow 

 for some portions of it to become clogged, and yet pass 

 the water through easily; this also diminishes the 

 chance of stoppage by its slower flow. A good form 

 for a small outlet is a trough, say six feet long by two 

 feet wide and twenty inches deep, with a dam near the 

 lower end about fifteen inches high. When the screens 

 are placed in this, above the dam, slanting the top down 

 stream at an angle of 45 degrees, it gives a good screen 

 surface, the dam being placed at the height at which 

 the water is to stand in the pond and the screen made to 

 slide between slats. Great care must be taken in setting 

 such a trough, if in earth, that the water does not work 

 around and under it, or that frost does not lift it out of 

 place ; the former may be provided for by wide flanges, 

 which make a sort of bulkhead and obstruct the direct 

 passage of crawfish, earthworms or other borers, which, 

 by starting a small leak, will soon cause a large one 

 before its presence is suspected. To guard against up- 

 heaval by frost, in a climate where the brook trout love 

 to dwell, is a more difficult matter ; but my own experi- 

 ence on this point leads to a preference for light soils 

 for tamping around the outlet box, instead of clay, 

 which I first used on account of its resistance to water, 

 but afterward abandoned, after a winter's fight with 

 frost, in favor^of a sandy, gravelly soil which was found 

 to serve the purpose as well, as far as the frost was con- 

 cerned, but which afforded excellent digging for the 

 crawfish (fresh-water lobster) with which the stream 

 was infested, and whose tunnels, once made in clay, 

 never by any chance closed up ; and, knowing their dis- 

 like to work in either sawdust or tanbark, a space of 

 about a foot was filled with these materials so that there 



