[31] INSTKUCTIONS FOE COLLECTING MOLLUSKS DALL. 



is in its i3roper position, and that the canvas strips are straightened 

 out behind the frame, can x)roceed to do his work. The dredge shonld 

 be put over the stern, the rudder having been unshipi^ed, and allowed 

 to sink gradually, the line being paid out quickly enough to allow the 

 frame to sink faster than the canvas attached to it. In this way foul- 

 ing will be avoided. The boat is better stationary while the dredge is 

 being dropped. Tlie long line used for the dredge is best of good soft 

 manila rope, about three quarters of an inch in diameter. It should be 

 coiled two or three times before beingused, to take out kinks. Although 

 a smaller line will do for shallow water, it is less convenient to handle. 

 If the depth is considerable and the dredger supplied with only a 

 moderate amount of line, it is perhaps best to fasten the inner end of 

 the long line to oue of the thwarts to avoid its being jerked overboard 

 by accident. When the dredge is felt to touch the bottom, the men can 

 begin pulling slowly. The dredger will pay out line enough in shallow 

 water to the amount of at least twice the depth; in deeper water three 

 times the depth may be needed. After some experience the dredger 

 will find that no absolute rule in this matter can be laid down; that he^ 

 will need a shorter line on muddy bottom than on hard bottom, in 

 shallow water than in deep water, and that he may find it convenient, 

 from time to time, to alter the amount of line paid out to meet the cir- 

 cumstances of the case. After the necessary line has been paid out 

 the dredger will allow it to pass over the stern of the boat in the notch 

 cut for the sculling oar, since, if the line is not amidships, it will be 

 impossible for the men pulling the boat to pull straight forward. A 

 turn may be taken around a cleat with the line, but the dredger should 

 take hold of the line outside of the cleat with his hand, and continue 

 to hold it. He will soon be able to recognize by the feeling of the line 

 whether the dredge is j)assiug over smooth bottom or rough bottom, 

 whether it is biting into the bottom or not, and so on. If, after start- 

 ing, the line remains quiet in the hand without transmitting any quiver- 

 ing motions, the dredge is probably not oa the bottom, and more line 

 requires to be paid out; or, if it is on the bottom, it is possible that it 

 may have become fouled so that nothing is getting into it. When it is 

 doing its duty, the dredger can not fail to perceive the peculiar sensa- 

 tions which are transmitted along the line. If the dredge catches on 

 anything which holds it, one or two quick jerks on the line will probably 

 release it. The length of time that the dredge should be towed varies 

 with the conditions. On gravelly bottom, mixed with mud, a compara- 

 tively short time will be necessary to fill the dredge, when it may be 

 hauled in. On sandy bottom, if it be not rich with life, the dredge may 

 be hauled for a long time before it accumulates any considerable amount 

 of material. All these things can be only briefly referred to here, since 

 they are much bettef learned by experience. When the dredger thinks 

 the time has come for hauling in, the rowers cease pulling, and he hauls 

 in the line until the dredge is on the top of the water ; but before taking 



