x CONTENTS. 



CHAPTER IV. 



CURRENTS. 



PAGE 



Origin of ocean currents Evaporation and precipitation Water-circulation 

 in Mediterranean and similar seas Effect of wind on currents Temporary 

 currents caused by wind Currents running counter to prevailing winds 

 Tidal currents " Races " or "roosts" Velocity of littoral currents 

 increased by breakwaters projected across them Effect of currents upon 

 height of waves Strong currents out of harbours objectionable . . G3 



CHAPTER V. 



FETCH, EXPOSURE, AND WAVE-POWER. 



Definition of " Fetch " Fetch alone no indication of exposure "Wheeling of 

 waves Direction of waves affected by contours of sea-bed Exposure of 

 sites affected by shift of wind and by scour during gales Glacial action 

 mistaken for wave-power Movement of earth's crust in relation to 

 apparent effects of wave-power Raised beaches Ruins of temple of 

 Jupiter Serapis Effect of waves on coast near Wick ; also at Holburn 

 Head, Caithness Effect of falling water Evidences of wave-power in 

 Zetland Wave-power as displayed at Ymuiden, Kurrachee, Wick, 

 Alderney, Scilly Isles, Wolf Rock lighthouse, etc. Mud as an indication 

 of exposure General remarks on exposure of sites 73 



CHAPTER VI 



QUARRYING. 



Selection of quarry site Overburden Drainage Arrangement of quarries- 

 Height of working face " Strike " and "dip" of strata Small-hole 

 blasting Weight of charges Mine-blasting Line of least resistance 

 Cranes, etc. Steam and hand drilling Consumption of steel Forms of 

 drills Explosives Seam-firing Cutting stone by means of " plugs " and 

 "feathers" Charging bore-holes Tamping Firing by electricity 

 Lightning fuse Safety fuse 89 



CHAPTER VJL 



MATERIALS. 



SECTION I. 



General remarks Erosion Eroding agents Power of moving shingle Sand- 

 blast Danger of open joints in structures 105 



SECTION II. STONE. 



Stone for sea-works should have high specific gravity Basalt, granites, and 

 syenites List of stones Indications of decay Chalk, limestones, and 

 sandstones Pholas dactylus Quartzite Weathering qualities of stones 

 Iron-furnace slag used for constructing breakwaters . . . .110 



SECTION III. CONCRETE. 



Early use of concrete Value of concrete in sea-works Hydraulic lime Pro- 

 portion of ingredients in concrete Mixing by hand Mixing by machines 

 Concrete-block making Roman-cement concrete Medina cement 

 Stone-faced blocks Blocks built of rubble in cement mortar . .- .113 



