256 HARBOUR CONSTRUCTION. 



embankment is formed. When this is done, the bank must be 

 kept at such a height above high water as to admit of lines of 

 railway being laid along it. 



This system is only applicable where the exposure is not 

 great. In a work exposed to a heavy sea, the expense resulting 

 from the displacement and washing away of the lines of way 

 would probably equal or exceed the cost of staging, especially if 

 the delays arising from such interruptions were taken into 

 account. 



The mound portion of the sea-wall at Port Elizabeth (Cape 

 Colony) was formed in this manner. It was nearly broadside 

 on to the waves, and was composed of rubble and concrete 

 blocks varying in weight from 7 tons downwards. The depth 

 of the water along the face of this bank did not usually 1 

 exceed 11 or 12 feet at high water; nevertheless long lengths 

 of rails and sleepers were often displaced, necessitating much 

 labour in making up the bank, and recovering, straightening, 

 and re-laying the rails, etc. 



Probably the largest breakwaters that have been formed in 

 this manner are those at the mouth of the River Tees. They 

 are composed of blocks of slag weighing about 3 tons each, 

 obtained from the iron furnaces of the district. The rubble 

 forming the breakwaters at Kingstown was also deposited in 

 this way. 



The over-end system is well adapted for river embankments 

 or training walls where the exposure is small. 



1 The sea-bed was of sand, and its level varied considerably, according to the 

 state of the weather. 



