15 Lacustrine clay at Skipsea 92 16 Clay at Nostel, showing Marine Band 94 17 Kaolinite and Mica 105 18 Mining best Potter's clay in Devonshire 111 THE CHIEF CLAY ROCKS (arranged geologically) +--------------------------------------------------------+ {|Recent (_alluvial clay_, _silt_, _brick earths_, | {| _boulder clay_) | {|--------------------------------------------------------| Tertiary {|Pliocene } | {|Miocene } (_brick earths_, _ball clays_, | {|Oligocene } _coarse pottery clays_) | {|Eocene } | |--------------------------------------------------------| {|Cretaceous (_cement clays_, _brick clays_) | {|--------------------------------------------------------| Secondary {|Oolitic (_brick and tile clays_) | {|--------------------------------------------------------| {|Triassic (_brick, tile and terra-cotta clays_) | |--------------------------------------------------------| {|Permian (_brick, tile and flower-pot clays_) | {|--------------------------------------------------------| {|Carboniferous (_brick clays_, _fireclays_, _ganister_) | {|--------------------------------------------------------| Primary {|Devonian } | {|Silurian } | {|Ordovician } (_clay schists, slates and clay shales_) | {|Cambrian } | {|Pre-Cambrian } | |--------------------------------------------------------| |Igneous Rocks occur on several horizons (_china clays_ | | _and kaolins_) | +--------------------------------------------------------+ (In the above Table only the clay-bearing strata are mentioned. The formations named consist chiefly of other rocks in which the clays form strata of variable thickness.) CHAPTER I INTRODUCTION. THE CHEMICAL AND PHYSICAL PROPERTIES OF CLAY The chief uses of clay have been recognized since the earliest periods of civilization; the ancient Assyrian and Egyptian records contain numerous references to the employment of clay for the manufacture of bricks and for fulling or whitening cloth.