ON COLLECTING SHELLS. 275 



said that man}- small valuable objects may be washed through 

 the meshes of the upper part of the dredge along with the mud, 

 and thus lost ; but on the other hand, if the bag be ver}'^ close 

 it is apt to get filled up with mud at once, and to collect nothing 

 more, 



"It is always well when dredging, at whatever depth, to ascer- 

 tain the approximate depth with the lead before casting the 

 dredge; and the lead ought alwa^ys to be accompanied b}- a 

 protected thermometer ; for the subsequent haul will gain greatly 

 in value as an observation in geographical distribution if it be 

 accompanied by an accurate note of the bottom temperature. 



" For depths under a hundred fathoms the amount of rope 

 paid out should be at least double the depth. Under thirty 

 fathoms, where one generally works more rapidl}^, it should be 

 more nearly three times. This gives a good deal of slack before 

 the dredge if the boat be moving very slowlj'-, and keeps the lip 

 of the dredge well down ; and if the boat be moving too quicklj' 

 through the water, by far the most common error in amateur 

 dredging, from the low angle at which the line is lying in the 

 water, the dredge has its best chance of getting an occasional 

 scrape. It is bad economy to use too light a rope. For a dredge 

 such as that described, and for work round the coasts, at a depth 

 attainable from a row-boat or yawl, I would recommend bolt- 

 rope of the best Russian hemp, not less than one and a half 

 inches in circumference, which should contain from eighteen to 

 twenty yarns in three strands. Each 3^arn should bear nearl}^ a 

 hundred-weight, so that the breaking strain of such a rope ought 

 to be upwards of a ton. Of course it is never voluntaril}^ exposed 

 to such a strain, but in shallow water the dredge is often caught 

 among rocks or coral, and the rope ought to be strong enough 

 in such a case to bring up the boat, even if there were some 

 little way on. 



" Dredging in sand or mud, the dredge rope may simply be 

 passed through the double eye formed by the extremities of the 

 two arms of the dredge ; but in rocky or unknown ground it is 

 better to fasten the rope to one of the eyes only, and to tie the 

 two eyes together with about three or four turns of rope yarn. 

 This iDreaks much more easilj^ than the dredge rope, so that if 

 the dredge gets caught it is the first thing to give way under a 

 strain, and in doing so it very often so alters the position and 

 form of the dredge as to allow of its extrication. 



" The dredge is slipped gently over the side or stern — in a 

 small boat more generally the latter — while there is a little way 

 on, and the direction which the rope takes indicates roughly 

 whether the dredge is going down properly. When it reaches 

 the ground and begins to scrape, an experienced hand upon the 

 rope can usually at once detect a tremor given to the di'edge 



