82 DEEDGING AT OBAN. 



GENEKAL EEPORT ON THE DREDGING OPERATIONS 

 AT OBAN OF THE BIRMINGHAM NATURAL HISTORY 

 AND MICROSCOPICAL SOCIETY, JULY 5th to 12th. 1«81. 



BY JOHN F. GOODE AND WILLIAM P. MARSHALL. 

 J!r>i>I hrjnrr t/i>' Sorieti/, Mnnh •?Z.s■^ 1882. 



In this Dred<^in.!J Excursion of the Society the operation of dredging 

 was carried on from a small screw steam-yacht, the " Curlew," Capt. 

 Adam, engaged for a week for this purpose, of about 20 tons burthen, 

 50ft. length, and !)ft. beam; speed about 10 miles an hour. From 

 nine to twelve dredgings per day were obtained in depths of water 

 varying from 15 to 53 fathoms, and most generally about 20 fathoms 

 depth. This steamer was found to be smaller in size than was 

 desirable for convenience of working, and for speed in getting out to 

 the dredging ground. 



The dredge-nets used were 2ft. wide and 2ft. long, with lOin. 

 opening between the steel-edged scrapers at the mouth ; a tangle, 16in. 

 long, was attached to each bottom corner of the net. Three dredges 

 were taken, two of them being genei'ally in use alternately with one 

 another. A length of 100 fathoms of 2^in. circumference rope was 

 taken out, and the whole length was required for the deepest dredging 

 taken, which was in 53 fathoms of water. One arm only of the dredge- 

 frame was made fast to the rope, the other arm being attached to the 

 rope by a lashing of small cord, calculated to break before any injurious 

 strain could come upon the rope ; and the utility of this provision was 

 experienced on one occasion when the dredge got jammed fast at the 

 bottom and the lashing parted, causing the dredge-frame to open, and 

 the net to come up empty but safe. 



When the dredge was hauled up the contents were emptied out for 

 examination upon a working table 3ft. wide and 4^ft. long, covered 

 with white oil-cloth, fastened down smooth. This was convenient for 

 sorting out the specimens and washing off the mud that was brought 

 up with them, and the end of the table projected over the side of the 

 vessel for discharging the debris continuously direct into the water. 

 Glazed iron pans, 16in. diameter and 3in. deep, were used in sorting 

 and cleaning the specimens, which were then put into wide-mouthed 

 glass jars of three sizes — Gin. diameter by lOin. high, 3Jin. by 8in., 

 and 2in. by 6in. The glass jars were kept in a box divided into 

 separate compartments for safe carriage, in which they were daily 

 brought to and from the steamer, and were finally packed for convey- 

 ing home the selected specimens transferred into spirit. Three 

 galvanised iron sieves were also used, having 1^, f, and ^■\. inch 

 meshes respectively. Four tow-nets were taken, 1ft. diameter and 2ft. 

 long, one made of coarse muslin, and the others of fine muslin ; these 

 were used occasionally, either from the steamer or from a rowing boat. 



When the dredge was lowered it was left each time from ten to 



