270 A TREATISE ON DREDGES AND DREDGING 



tion of siind and gravel, up to the level of the original hike bottom, 

 this material having been back filled into a trench dredged practically 

 to bed rock. At the outer end of the breakwater, where the water 

 is over 22 ft. deep (also the maximum depth of the timber cribs), 

 a rubble stone foundation is interposed between the bottom of the 

 cribs and the top of the gravel filling. 



"The South Harbor timber breakwater also stands upon a similar 

 artificial foundation, with the exception that the rubble stone 

 foundation is almost uniformly 8 ft. high, the cribs resting directly 

 upon this. 



"Under the original specifications contractors were permitted 

 to use either hydraulic dredges or the clamshell type. 



"The successful contractors, Hughes Bros. & Bangs, elected to 

 excavate the trenches by means of a very large clamshell dredge, 

 built expressly for this work by the Osgood Dredge Co., of Albany, 

 N. Y. 



"'This dredge was illustrated and fully described in Engineering 

 News of February 2, 1899, while it was engaged on the Buffalo works. 

 It may be noted here that the clamshell bucket of this dredge 

 has a capacity of 10 cu.yds. and weighed empty over 30,000 Ibs. 

 The hull of the dredge is 120 ft. long and 40 ft. broad., and a 

 false stern increases the total length to 151 ft. The dredge had 

 to excavate material from depths up to 70 ft., much of it 

 solidly compacted. Most of the material dredged was a moderately 

 stiff red clay, mixed with some blue clay. Overlying this clay 

 was a layer of sand, perhaps one or two feet thick. Underlying 

 the clay next to the rock was a layer of hard blue clay, mixed 

 with broken stone or gravel, and in places there were a good 

 many large boulders. 



"The dredged material was generally transported to a dumping 

 ground 10,000 ft. distant from the dredge, the time for the round 

 trip being 1 hour and 6 minutes. Three steel scows were used to 

 transport the excavated material. 



"The principal cause of delay was the sen and wind (about tliree- 

 eighths of the total delays). Considerable delay was also due to 

 the clamshell bucket. Moving and placing the dredge was another 

 large item of delay. 



"Generally the dredge lay at anchor, in working position, through- 

 out the week, and on Sundays was towed to shelter behind the com- 

 pleted Stony Point breakwater. This was al.-o done during stonns. 



