Mafic 



Refers to ferromagnesian minerals in a rock. 



Malacology 



The division of zoology that deals with mollusks. 



Mallee 



Scrub vegetation composed largely of various species of 

 Eucalyptus, about 2 to 10 meters high, in dry, subtropical 

 parts of southwest and southeast Australia. 



Malthusian 



Refers to the doctrine of T. R. Malthus that organisms 

 tend to increase in geometrical progression while the food 

 supply increases in arithmetical progression, so that the in- 

 crease in the size of a population tends to be at a more rapid 

 rate than the increase in available food. cf. Competition. 



Mammal 



An animal in the class Mammalia, subphylum Vertebrata, 

 e.g., rabbit, deer. 



Mangrove 



A type of vegetation that is worldwide on tropical and 

 subtropical saline, tidal mud flats, consisting usually of low 

 trees or shrubs in genera Rhizopora, Avicennia, and 

 Sonneratia. 



Maquis 



See Macchia. 



Marl 



A deposit of chiefly calcium carbonate, mixed with clay 

 or other material, and formed chiefly in fresh water lakes 

 by organisms such as Chara. 



Marsh 



A Swamp in which grasses, sedges, cattails, or rushes form 

 the dominant vegetation, cf. Bog. Moor. 



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