360 PRACTICAL LESSONS IN SCIENCE. 



age, as the Green river and Uintah basins of the eocene ; basins 

 in Nebraska and Oregon belonging to the miocene; the Nio- 

 brara and White river basins and others containing pliocene 

 deposits. 



The rocks of the tertiary consist of beds of sand and clay, 

 shell beds and marls, compact sandstones, calcareous sandstones 

 and limestones. On the Pacific slope some metamorphic rocks 

 are found, metamorphic agencies having been in force in that 

 region after some of the tertiary sediments had been deposited. 

 Some coal in the Western mountain system is referred to this 

 period . 



Among plants, the genera of the dicotyledons, palms and 

 grasses were about the same as now, but most of the species were 

 different from those of the present. Magnolias, palms and other 

 sub-tropical plants grew in the extreme north of Europe and 

 North America, indicating a much warmer climate than now pre- 

 vails in those regions. Immense deposits of infusorial earth, 

 composed largely of diatom shells, indicate an abundance of 

 microscopic life. 



Among animals, mollusks, insects, worms and fish were abun- 

 dant ; reptiles and birds were numerous, but mammals were the 

 characteristic and dominant form of life. Herbivorous animals, 

 like the rhinoceros, mastodon, elephant, camel, giraffe, tapir, 

 antelope, hog and horse were common. From the Green river 

 and adjacent basins more than 150 species of vertebrates have 

 been described. Carnivorous animals, like the tiger, panther, 

 wolf, fox and hyena were abundant, and remains of animals like 

 the beaver and porcupine have been found. 



Quite a series of the ancestors of the modern horse have 

 been found in these rocks, beginning with one having four 

 toes, and gradually diminishing till the present form, with one 

 toe, is reached. The horse and camel seem to have originated on 

 this continent; and the number of old-world forms found in the 

 rocks of North America would indicate free communication be- 

 tween the continents through long periods of time. The nearly 

 common forest vegetation prevailing through the northern 



