THE CALIFOKNIAN SALMON. 
85 
otherwise run to waste, to keep up the supply in the dry 
season. The channel o£ the brook is a rocky glen 
or [gorge, and in some places the stream runs under- 
neath large rocks, and into cavernous recesses, which lowers 
the temperature of the water, even in very hot weather, most 
remarkably. I have found the water at the surface of the 
dam 79 deg., and flowing over the sluice gate at this tem- 
perature, and it was reduced in a distance of 200 yards 
lower down the glen, at the hatching-boxes, to 57 deg. The 
bottom temperature of the dam also, during all the early 
part of the summer, keeps very low, being 55 deg. at five 
feet beneath the surface, while the stream from springs 
running into the dam was 80 deg., and the surface stratum 
of water in it of the same temperature. On making the 
discovery that there was this difference of 25 deg. between 
the top and bottom temperature, I arranged so as to 
draw off the water from the bottom of the dam, instead of 
allowing it to overflow at the sluice-gate, and thus, by 
maintaining a lower temperature in the hatching-boxes, 
contributed greatly to the success of my undertaking. 
The water of this stream is dammed up by a little stone 
and cement work under a rock, and carried by a two-inch 
galvanised iron pipe, which is covered with a hay-rope wound 
round it to protect it from the sun and to keep down the 
temperature. The hatching-boxes are seven in number, 
and in addition to them, I had a stone and cement race 
constructed on the ground, divided down the centre, and so 
arranged that the water would circulate with a gentle 
current through all the boxes, up one side of the race 
and down the other ; there are little miniature waterfalls 
from one box to another, to aerate the water, which 
finally flows through four small ponds, fitted with gratings 
■to retain the young fish, when they are sufficiently 
advanced to require this precaution, and covered with 
