402 NATURAL HISTORY. 



Alluvium or Vegetable Earth, which is a combina- 

 tion of different earths or soils, varying according to cir- 

 cumstances or position. Mostly it is composed of 

 mixture of sand, clay, and marl, but is also very often 

 formed directly by the disintegration of other formations. 

 and their mixture with the products of decomposition of 

 other plants and animals, spread in a layer of more or 

 less thickness, over the surface of the earth is called 

 Humus. Wherever this deposit is found abundantly, 

 the soil is eminently fruitful. 



Turf Moors or Peat Bogs are found in different ex- 

 cavations of the surfa'ce in valleys or low marshy situa- 

 tions, where stagnant waters constantly exist. All 

 aquatic plants, such as Duck-meat (Lemma), cresses, 

 etc., contribute to the formation of peat, as well as ter- 

 restrial plants brought to these bogs by brooks, and, 

 being submerged, gradually become decomposed, and 

 form a single accumulated mass of what seems black 

 earth. From this soil spring various other plants, 

 which, in their turn die and also become decomposed, 

 particularly as the water partially dries away. Fre- 

 quently trees or large plants which grow on the borders 

 are found buried in the mass, particularly in the lower 

 part, where they accumulate on sands and clays found 

 on the bottom, or, mingling Avith the humus, compose a 

 web of fibrous tissue, which forms the combustible sub- 

 stance known as peat or turf. These peat-bogs, when 

 exhausted, if left undisturbed for a few years, are sure 

 to renew themselves by a similar process to that already 

 described. 



Coral Reefs. These formations of stony polyparia are 

 the framework formed by coral animalcule, and cemented 

 together by calcareous matter. The polyparia continue 



