194 NEW TRACKS IN NORTH AMERICA, 
relied upon, most of the rich, well-watered placers were soo 
exhausted, and it was necessary that some means should be 
devised for directing water to less-favoured districts. This 
led to the introduction of mining ditches to carry water from 
the highest springs in the hills to the auriferous ground a 
their base. Such ditches were expensive, for the water had 
to be brought in “flumes” for miles across ravines 200 0 
300 feet deep, along thé rugged mountain-sides, and often 
through rock cuttings; and the capital required to make 
these aqueducts had usually to be borrowed at the rate of 
from 3 to 10 per cent. per month. ‘ 
With the mining ditches came the “tom” and sluice. The 
tom is a trough twenty feet long and eight fect deep; it is! 
fifteen inches wide at the head and thirty at the foot. This | 
trough rests upon a flat box; its bottom is formed of sheet-. 
iron pierced with holes, through which the pay dirt is 
washed by a constant stream of water. The gold is caught 
by transverse “cleets,” or « riffles,” which rise from the 
bottom of the box, and all the pay dirt which passes over the 
tom undecomposed is again thrown back, to go through. 
the same process again. The sluice is the box of the tom in| 
principle, elongated to any length from 100 to 1,000 feet ; 
it has transverse cleets along its whole length, to catch the | 
gold, and is placed at an inclination of one in twenty, so as | 
to cause the water to rush through it like a torrent. This 
