THE ELEMENTS OF ECONOMIC GEOLOGY
CHAPTER XV
PAGE
THE GEOLOGY OF CEMENTS . . 185
Definition and Groups of Cements. Hydraulic and Portland
Cements. Price. Gypsum Cements— Plaster of Paris.
CHAPTER XVI

THE SoIL . . 19
Definition and Function. Soil Constitution—Sand, Clay, and Silt.
Soil Composition. Soil Texture and Water Capacity. Soil
Composition and Surveys.

CHAPTER XVII

MINERAL FERTILIZERS—NITRATES AND PHOSPHATES . . I
Nitrates characteristic of Arid Areas. Theories of Formation.
Phosphates—Value and Use of Phosphorus. Apatite Veins.
Guano. Rock Phosphates. Lagoon Phosphate. Granular
Phosphates and Phosphatic Chalk.
CHAPTER XVIII

THE SALT DEPOSITS 3 . . 206
Composition of Sea-water. Concentration in Salt Lakes, The
German Salt Fields. Intrusive Salt Deposits and Salt
Domes. Potash Salts—value in Agriculture, Derived from
Sea-water. Secondary Concentrations.

ENGINEERING GEOLOGY
CHAPTER XIX

PART 1V

WATER SUPPLY ; . 2I¢
Three Sources of Water—Meteoric, Connate, Plutonic or Juvenile,
Disposal of Rainfall—Run-off, Evaporation, Percolation,
Circulation of Subterranean Water— Piezometers. The Yield
of Wells—Water-storage. Wells and Springs. Flowing
Wells. Rock Pressure. Gas Pressure. Town Supplies and
Settlement. Reservoir Sites,
CHAPTER XX

CoAST DEFENCE, COASTAL WORKS, AND RECLAMATION . . 238
Waves and Wave Action. Recession of the Land. Transport of
Beach Material, Continental Shelf. Rate of Marine Abra.
sion, Coastal Accretion. Warping—the Silting of Estuaries.
Coastal Protection by Planting and Groynes. Sea Walls,
Estuary Works and Models.