The processes of supply of elements to the sea floor will determine the occurrence of these deposits. Chemical elements enter seawater in a num-ber of different ways. Sometimes their ultimate source is the dissolved material in rivers draining the continents. In other cases, they are derived from hydrothermal solutions entering seawater from submarine volca-noes. …
In one of those beautiful valleys, through which the Thames (not yet polluted by the tide, the scouring of cities, or even the minor defilement of the sandy streams of Surrey) rolls a clear flood through flowery meadows, under the shade of old beech woods, and the smooth mossy greensward of the chalk hills (which pour into it their tributary rivulets, as pure and pellucid as the fountain of…