QUATERNARY AGE. — GLACIAL PERIOD. 527 



Australian feature also may have been a result of migration, but from 

 the opposite direction. The Indian Ocean currents favor migration 

 northward, along the borders of Asia, and not that in the opposite 

 direction. 



II. THE QUATERNARY AGE, AND ERA OF MAN. 



Hitherto, through the ages, to the close of the Tertiary period, the 

 continent of North America had been receiving a gradual extension 

 to the southward, spreading itself southeastward on the Atlantic side, 

 and southwestward on the Pacific. The scene of prominent action 

 here changes ; and, in the Quaternary, the great phenomena are mainly 

 northern. The same general fact is true for all the continents, north 

 and south : the changes affect most decidedly the higher latitudes of 

 the globe. The Quaternary in America includes three periods : — 



1. The Glacial, or that of the Drift; 2, the Champlain, and 3, 

 the Recent or Terrace. 



1. GLACIAL PERIOD. 

 1. American. 



L Material, Phenomena, and Distribution of the Drift. 



1. Drift. — The term Drift, as it is commonly employed in Geol- 

 ogy, includes the gravel, sand, clay, and bowlders, occurring unstrati- 

 fied, or without order of arrangement, over some parts of the conti- 

 nents, which have been transported from places commonly in higher 

 latitudes, by some agency which (1) could carry masses of rock hun- 

 dreds of tons in weight, and which (2) was not alwaj^s dependent for 

 motion on the slopes of the surface. 



Other portions of the same transported material are stratified sands, 

 clays, pebble beds, and cobble-stone beds ; and these are stratified 

 Drift. The latter is sometimes called modified Drift ; but the mate- 

 rial was often stratified in its first deposition, making the term modi- 

 fied inapplicable. The lower part of the unstratified Drift, is often a 

 bed of clay, containing stones or bowlders, called the bowlder clay. 



The unstratified and also the stratified Drift, over the interior of the 

 continent, contain no marine fossils ; while drifted logs and other ac- 

 cumulations of vegetable material, and, in the stratified, fresh-water or 

 land shells, are not uncommon. Toward or along the sea-shores, the 

 stratified beds often contain marine shells. 



Nearly all the stratified Drift, and a large part of the unstratified, 

 were deposited during the Champlain period ; and hence the descrip- 

 tion of the former is given with the account of that period. 



