546 THE CRETACEOUS PERIOD 



dioxide in the carbonation of rock, there was a combination of 

 conditions regarded as favorable for a mild and uniform climate. 



LIFE 



Land plants. Angiosperms predominated in North America at 

 the beginning of the Cretaceous, and during the period genera now 

 living came to be numerous, giving the flora a modern aspect. 

 Among the living genera which made their appearance were those 

 which include the birch, beech, oak, walnut, sycamore, tulip-tree, 

 and maple. Among the gymnosperms there was a notable devel- 

 opment of the sequoias, which now include the giant trees of Cali- 

 fornia. Of special interest was the presence of genera in Europe and 

 the United States which are now confined to the southern hemi- 

 sphere. 



Toward the close of this period, monocotyledons first became 

 abundant, so far as the record shows. Palms were plentiful, even 

 in northerly latitudes, before the close of the period. Of greater 

 importance because of their relations to the evolution of grazing 

 animals, was the appearance of grasses, which attained prominence 

 later. 



It is worthy of remark that the introduction of dicotyledons, 

 the great bearers of fruits and nuts, and of monocotyledons, the 

 greatest grain and fodder producers, was the groundwork for a 

 profound evolution of land animals. A zoological revolution, as 

 extraordinary as the botanical one, might naturally be anticipated; 

 but it did not follow immediately, so far as the record shows. The 

 reptiles seem to have roamed through the new forests as they had 

 through the old, without radical modification. But with the open- 

 ing of the next era, the anticipated revolution in the animal life of 

 the land made its appearance, and advanced with great rapidity. 



The new flora spread widely. The European flora was very 

 much like the American, and there was a close resemblance between 

 the plants of mid-Greenland ('jo-'j2 Lat.) and those of Virginia, 

 indicating climatic conditions of remarkable uniformity. Not only 

 this, but the flora was of a sub-tropical type. 



Land animals. The terrestrial animals had the same general 

 aspect as in the preceding period. Dinosaurs still retained the lead- 

 ing place among land reptiles, though carnivorous forms were less 

 abundant and varied than before. Among them was a leaping, 

 kangaroo-like form with a length of 15 feet. The most singular 



