206 THE DEPTHS OF THE SEA. (CHAP. V. 
The ordinary deep-sea lead is a prismatic leaden 
block about two feet in length and 80 to 120 lbs. in 
weight, narrowing somewhat towards the upper end, 
where it is furnished with a stout iron ring. Before 
heaving, the lead is ‘ armed,’ that is to say the lower 
end, which is slightly cupped, is covered with a thick 
coating of soft tallow. If the lead reach the bottom 
it brings up evidence of its having done so in a 
sample sticking to the tallow. Usually there is 
enough to indicate roughly the nature of the ground, 
and it is on the evidence of samples thus brought 
up on the ‘arming’ of the lead that our charts note 
‘mud,’ ‘ shells,’ ‘ gravel,’ ‘ ooze,’ or ‘sand,’ or a com- 
bination of these, as the kind of bottom at the 
particular sounding ; thus we have ,,?s°,, mud, shells, 
and sand at 2,000 fathoms; 2°, ooze and stones at 
2,050 fathoms; ,, 2’ sc., mud, sand, shells, and scorize 
at 2,200 fathoms, and so on. 
When no bottom is found, that is to say, when 
there is no arrest to the running out of the line and 
nothing on the ‘arming’ of the lead, the sounding 
is entered on the chart thus, 33, no bottom at 3,200 
fathoms. Such soundings are not to be depended 
upon in deep water, but they are usually quite 
reliable for moderate depths, so far as they go. They 
give us no help in the exploration of the bottom of 
the sea, but they are of great practical value, and 
indeed they give all the information which is directly 
required for the purposes of navigation; for if there 
be ‘no bottom’ at 200 fathoms, there is probably no 
dangerous shoal in the immediate neighbourhood. 
Soundings are usually taken from the vessel, and 
while there is some way on. Where great accuracy 
