54 THE SALMON FISHERIES. 
the cost of a dam double that height. A baulk of timber 
fixed diagonally across the face of the sloping apron of a 
weir—as at Bransford Weir on the Teme, a tributary of the 
Severn, or at Lowood Weir on the River Leven—so as to 
collect into a small stream the water which would other- 
wise trickle down the slope in a thin sheet, may make a 
very efficient pass at a cost of a few pounds, 
Another simple method of passing fish over a dam is to 
erect a short distance below it a second or subsidiary dam, 
which will have the effect of backing up the water against 
the obstruction above, and so of reducing the height which 
the fish have to jump. A third dam may, if necessary, be 
built below the second, and thus a single high fall may be 
converted into two or three jumps of half or one-third its 
original height. This plan is only an extension of the 
principle on which the Ballisodare ladders are made. The 
whole volume of the river itself is made into a ladder with a 
series of broad and wide steps, up which the salmon leap 
with more or less ease, according to their height. Passes 
on this principle have been successfully adopted at Chol- 
lerford and Otterburn dams, on tributaries of the North 
Tyne, at Levenshall dam on the Kent, and at other 
places. 
The advantages of this system are that it involves no 
interference with the structure of the original dam, and that 
it affords roomy pools in which the fish may lie. Its dis- 
advantages are its cost in the case ofa wide and rapid stream, 
and the possibility of the new weirs under certain circum- 
stances causing the adjacent lands to be flooded. The great 
advantage, however, of this form of pass is that, in the case 
of a mill-dam, the first subsidiary weir may be built at such a 
spot as to intercept the water from the tail race of the mill; 
and thus the whole volume of the river, whether the mill is 
