CHAP. vi.J DEEP-SEA DREDGING. 243 



bags. Raw buffalo- and cow-hides are very strong-, 

 but they are apt to become offensive. When these 

 are used it is necessary to punch holes here and there 

 to let the water through or to leave the seams which 

 are sewed with thongs a little open. Another bag 

 which I have used frequently is made of sail-cloth, 

 with a window of strong brass wire gauze let in on 

 either side. Nothing, however, seems to me so good 

 as strong cord netting. The water passes easily 

 through and carries with it a large part of the fine 

 mud, while enough mud is retained by the bread- 

 bag lining in the bottom to give a fair sample of its 

 contents. It may be said that many 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 very 

 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 ascertain the approximate depth with the 

 lead before casting the dredge ; and the lead ought 

 always to be accompanied by a protected thermome 

 ter, for the subsequent haul of the dredge 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 100 

 fathoms the amount of rope paid out should be at 

 least double the depth. Under thirty fathoms, where 

 one generally works more rapidly, it should be more 

 nearly three times. This gives a good deal of slack 

 before the dredge if the boat be moving very slowly, 

 and keeps the lip of the dredge well down ; and if the 

 boat be moving too quickly through the water, by 



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