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256 THE DEPTHS OF THE SEA. [CHAP. VI. 
Captain Calver sent down half-a-dozen of the ‘ swabs’ 
used for washing the decks attached to the dredge. 
The result was marvellous. The tangled hemp 
brought up everything rough and moveable which 
came in its way, and swept the bottom as it might 
have swept the deck. Captain Calver’s invention 
initiated a new era _in deep-sea dredging. After 
Various experiments we came to the conclusion that 
the best plan was to attach a long iron transverse bar 
to the bottom of the dredge-bag, and to fasten large 
bunches of teazed-out hemp to the free ends of the 
bar (Fig. 51). We now regard the ‘ hempen tangles ’ 
as an essential adjunct to the dredge nearly as 
important as the dredge itself, and usually much 
more conspicuous in its results. Sometimes, when 
the ground is too rough for ordinary dredging, we 
use the tangles alone. There is some danger, how- 
ever, in their use. The dredgé employed under the 
most favourable circumstances may be supposed or 
hoped to pass over the surface of the floor of the 
sea for a certain distance, picking up the objects in 
its path which are perfectly free, and small enough 
to enter the dredge mouth. If they chance to be 
attached in any way, the dredge rides over them. 
If they exceed in the least the width of the dredge- 
opening, at the particular angle at which the dredge 
may present itself at the moment, they are shoved 
aside and lost. 
The Mollusca have by far the best chance of being 
fully represented in investigations carried on by the 
dredge alone. Their shells are comparatively small 
solid bodies mixed with the stones on the bottom, 
and they enter the dredge along with these. Echino- 
