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 Ibs. 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 m 2 ' s hs. 5 mud, shells, 

 and sand at 2,000 fathoms ; ^11 .> ooze and stones at 

 2,050 fathoms; m . S 2 ' 2 s hsc.j mud, sand, shells, and scoriaB 

 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 no thing on the 'arming' of the lead, the sounding 

 is entered on the chart thus, 3 -^ , 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 



