464 ESSENTIALS OF ZOOLOGY 



3. The Deciduous Forest Formation (Oak-Deer Biome). — Most of 

 the United States lying east of the Mississippi River is characterized 

 by deciduous forest. . In this area the dominant vegetation consists 

 of trees whose leaves are shed during the unfavorable winter sea- 

 son, such as oaks, beech, maple, hickory, and elm. The most wide- 

 spread large herbivorous animal is the Virginia deer, although the 

 wapiti (elk) was formerly of frequent occurrence. The wolf and 

 the cougar were once widely distributed but are almost extinct now. 

 The bay lynx, a close relative of the Canada lynx, preys upon the 

 numerous rodents and birds. Other characteristic animals are the 

 opossum, the raccoon, the flying squirrel, and the woodchuck. Many 

 of these inhabit open areas in the woods rather than the dense forest. 



4. The Grassland Formation (Grass-Bison Biome). — No single 

 grass is included in the ''common" name of this community because 

 it is probable that the name of no single genus of grass is sufficiently 

 familiar. Important grasses in the great central grassland area are 

 the bluestems (or beard grasses), June grass, porcupine grass, grama 

 grass, and buffalo grass. The grassland region was the habitat of 

 the bison which once ranged over the prairies from Texas to Sas- 

 katchewan in enormous numbers. It is estimated that at the com- 

 ing of the white man there were over 75 million of these animals, 

 upon which the plains Indians depended for food, clothing, and 

 shelter. The American pronghorn or antelope was also abundant. 

 Both were held in check by the gray wolf. The black-tailed jack 

 rabbit is an animal of the open grassland while the cottontail oc- 

 cupies wooded or at least bushy areas. In the drier Avestern portion 

 of the grassland the prairie dog and the badger are common. There 

 are many small rodents, including the pocket gopher, the ground 

 squirrels, and prairie deer mice. 



5. The Sagebrush Formation (Sagebrush- Jack Rabbit Biome). — 

 This community is centered in the Great Basin of Nevada, Utah, 

 and neighboring states. It is an area of deficient rainfall, and 

 sagebrush is a prominent constituent of the vegetation. Most of 

 the larger animals belong to groups which are also found in neigh- 

 boring formations, although the smaller mammals are mostly of 

 different subspecies. Rabbits and rodents are especially abundant. 



6. The Desert Formation (Creosote Bush-Kangaroo Rat Biome). — 

 It is difficult to characterize this community by the name of a domi- 

 nant plant and an important mammal, as there are many types of 



