CENOZOIC ERA. AGE OF MAMMALS. 385 



the land along the border, until, at the end of the Ter- 

 tiary, the continent was finished, except the southern 

 part of Florida and its keys, and a very narrow strip 

 along the Southern coast generally. The southern point 

 and the keys of Florida are still growing (see page 111). 



SECTION II. QUATERNARY PERIOD. 



This is one of the most interesting and yet most diffi- 

 cult portions of the history of the earth. It is the last 

 period preceding and preparatory to the present. 



Characteristics. The grand characteristic of this pe- 

 riod is the occurrence of wide-spread up-and-down move- 

 ments of the earth's crust in high latitudes or circum- 

 polar regions north and south, attended with great 

 changes of climate from extreme rigor to temperateness, 

 and consequent great changes in species. Also, the age 

 of mammals seems to culminate here, and man appears 

 on the scene, and was doubtless an important agent 

 among others in bringing about the change of species. 

 Nearly all the invertebrate species and some mammals of 

 the Quaternary are still living. A small percentage of 

 the present mammalian species, man among the number, 

 commenced here (see Fig. 325, page 364). 



Subdivisions. The Quaternary period is divided into 

 two epochs, founded upon the attitude of the land and 

 the changes of climate. These are 1. Glacial. 2. Cham- 

 plain. The Glacial epoch was characterized by upward 

 crust-movement in high-latitude regions, until the land 

 there stood 2,000 to 3,000 feet higher than now, was 

 sheeted with ice, and an Arctic rigor of climate extended 

 in America almost to the shores of the Gulf. The Cham- 

 plain epoch was characterized by a downward movement 

 in the same region until the land was 500 to 1,000 feet 

 lower than now, so that many lower parts of the conti- 

 nent were covered with sea ; and by a moderation of tern- 



LE CONTE, GEOL. 25 



