G.— ENGINEERING. 125 



so consolidated itself as it falls upon the bed of the Pacific Ocean, and 

 has so filtered out all its lighter particles on its way, that its consolidation 

 has become very dense ; so much so that the fluke of an anchor let fall 

 upon it does not penetrate into its surface. This sandbank has been 

 brought uj) to a depth below water of 63 feet and graded quarried rock 

 is sjjread upon its top. Firstly, what is practically quarry rubbish of 

 variable sizes weighing about 2 tons per ni^, from which has been picked 

 the larger rubble, is spread on the toj) of the sandbank ; then upon this 

 quarry rubbish selected rock gradually increasing in dimensions as it 

 gets nearer low water (which weighs about 1"7 tons per m^) is placed. 

 The quarry rubbish (or what is known in Chile as ' desmontes ') is brought 

 up to 66 feet below low water level, and thereon the larger categories of 

 rock of 2 cwt. to 1|- tons and from IJ tons to 10 tons in weight to 39 ft. 6 in. 

 below low water are placed. This upper layer, containing the larger 

 categories, is deposited in excess to allow for settlement. It is levelled 

 by divers, and upon this surface are placed blocks weighing 60 tons upon 

 a slope of about 70° to the horizontal and at right angles to the axis of 

 the breakwater, interlocked on the inclined face throughout their depth, 

 so that they can slide down and take up any settlements in the bank on 

 which they rest. Before the 60-ton blocks are placed a period of one year 

 is allowed to elapse, so that the whole bank can settle. Notwithstanding 

 this period of one year the great weight of the superstructure does cause 

 further settlement, extending over some months, resulting in a final settle- 

 ment of about 3 feet. 



None of the different categories of material appear to have been moved 

 by the very heavy storms, locally known as ' northers ' on the western coast 

 of South America, neither have any tidal waves disturbed or earthquakes 

 moved, as far as we can determine, this enormous bank to any serious 

 extent. There is evidence of two earthquakes having occurred before 

 the breakwater was completed which caused some relatively small 

 disturbance of the sandbank. The rubble was deposited in its various 

 categories by hopper barges, and in its passage through the water there 

 is little doubt that anything of an earthy nature that might have adhered 

 to the rock was washed off it. This has, no doubt, contributed to its 

 solidity. 



Valparaiso is the first large breakwater in which a sand foundation has 

 been adopted to so large an extent, and there seems to be no doubt that 

 in suitable situations, and in a sufficient depth of water, smaller material 

 can be used for marine structures than has hitherto been employed. In 

 shoal water, or near the low-water level, or where currents exist, sand 

 should not be used. Small material may be satisfactory, however, at 

 great depths, as evidenced in Valparaiso. Masses of sixty tons are needed 

 on the Pacific Coast where, as on any coast, the vertical motion of the 

 waves is converted by the shoaling bottom into a horizontal one. If local 

 rock strata will not produce quarried rubble of sufficiently large categories, 

 which is the case with a great many of the rocky formations on the Pacific 

 Coast (due, no doubt, to earthquakes, which are numerous) artificial 

 concrete blocks are essential to produce the necessary masses. 



Experience at Dover Harbour, and also at Valparaiso, indicates that 

 below a level of forty-five feet, even in structures composed of practically 



