STIRRING DREDGES 141 



River, by Mr. J. A. Ockerson, C. E., Trans. Am. Soc. G. E., Vol. XL. 

 This long list of patents is due, so Mr. Ockerson says, to the fact that 

 the United States Government offered a premium of SI 00, 000 for 

 the best means of removing the sand-bars alongt he Mississippi 

 River. No wonder that the attention of so many inventors was 

 turned in this direction. 



Harrows and Scrapers. Since the Middle of the 14th century 

 the Venetians have employed the stirring process for the removal 

 of sand-bars which were formed by the accumulated deposits of 

 the tide, and they made use of the ebb tide as a vehicle to transport 

 the materials away from the point of excavation. At that time 

 the stirring was done by scraping the bottom with iron harrows 

 attached to long wooden handles. They were operated by men in 

 small boats. The operation was carried on during the ebb tide 

 only, so that the suspended materials were carried out to sea by 

 the receding water. 



The method was used in England years ago. Mr. Cresy, in 

 his Encyclopedia of Civil Engineering, thus describes the Floating 

 Clough, a machine used for scouring out the channel of the river 

 at Great Grimsby and also on the Humber. The scraper used was a 

 frame 12 ft. long, 9 ft. wide and 6 ft. deep of 6 x 4-in. timber, covered 

 with 2-in. plank, through the middle of which was a culvert 2 ft. 

 6 in. wide, made of planks, with a small lifting door at one end. 

 At the bottom two beams projected in front, serving as feelers to 

 keep the machine in its right position. In front are placed frames 

 of timber shod with iron, cut in a serrated form, which, by means 

 of a lever, can be raised at pleasure. At the sides of the machine 

 are wings, sloped to accommodate themselves to the fall of the banks. 

 The machine is moored in the middle of the stream, with the wings 

 extended by means of ropes, and at half flood the water is admitted 

 into the scraper by removing the plugs, and the machine sinks to 

 the bottom ; the plugs are then replaced, and the scraper remains in 

 this position till flood tide. The iron-shod frame, with teeth like a 

 saw, are let down in front, and the whole machine, being forced 

 along by the tide, scrapes up the bottom, and the mud disturbed is 

 carried along by the receding tide for a distance of three miles or 

 more in the space of two hours. 



In the United States the method of dredging by stirring up 

 the materials was successfully employed in the improvement of 

 the mouth of the Mississippi River. In the years 1853-1858 



