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 ini- 

 tiated a new era in deep-sea dredging. After various 

 experiments Ave 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). AVe 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, Ave 

 use the tangles alone. There is some danger, hoAV- 

 ever, in their use. The dredge 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 Avay, 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 haA r e by far the best chance of being 

 fully represented in investigations carried on by the 

 dredge alone. Their shells are comparatiA'ely small 

 solid bodies mixed with the stones on the bottom, 

 and they enter the dredge along with these. Echino- 



