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. 



I. Material, Phenomena, and Distribution of the Drift. 



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

 ology, includes the gravel, sand, clay, and bowlders, occurring over 

 some parts of the continents, which are without stratification or order 

 of arrangement, and have been transported from places in higher lati- 

 tudes, by some agency which (1) could carry masses of rock hundreds 

 of tons in weight, and which (2) was not always dependent for mo- 

 tion on the slopes of the surface. 



Other portions of the same transported material are stratified sands, 

 clays, pebble beds, and cobble-stone beds ; so that there is both un- 

 stratified and stratified Drift. 



The lower part of the unstratified Drift is generally a bed of un- 

 stratified clay. This clay usually contains stones, or bowlders, and is 

 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 their accu- 

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

 land shells are not uncommon. Toward or along the seashores, 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 descrh> 

 tion of the former is given with the account of that f>eriod. 



