Structure of Ihc Earth. 



379 



^/^lluvial or Diluvial^ is caused by the Avearing down of the 

 rocks, by the action of the weather and other causes, and the 

 washing away of the worn materials by rains and streams of wa- 

 ter. Considerable portions of many countries are covered with 

 thick beds of it, which consist of beds of sand or clay, fragments 

 of rock and loose stones, more or less rounded by attrition. In 

 some situations these have evidently been transported from a vast 

 distance, for frequently no rock similar to the fragments occurs 

 within a hundred miles, or more, of the place where they are de- 

 posited. They indicate the action of mighty inundations which 

 have swept over the face of our present continents. 



The classes of rocks above enumerated have their appropriate 

 mineral productions, and with the exception of rocks of the first 

 class their appropriate organic remains; and it would be as useless 

 to search for regular beds of common coal in the primary rocks, 

 as it would be to search for metallic veins or statuary marble, in 

 the tertiary strata. 



The following plate represents a section of the earth between 

 40° and 45° north latitude. Fig. I denotes the primary forma- 

 tion; 2, transition; 3, the lower secondary; 4, the upper secon- 

 dary; 5, tertiary; and 6, alluvial or diluvial formation. 



,^^^ ^;[?^^ 



I Alluvial is derived from the Latin, alluvia, au inundation of water. 

 Diluvial is from the Latin^ diluvium, the deluge or food. 



