386 HISTORICAL GEOLOGY. 



peratnre, a melting of ice, and a flooding of lakes and 

 rivers. It was therefore a flooded epoch. Loosened 

 icebergs floated over the flooded seas and lakes. It was 

 therefore,, also, an epoch of the reign of icebergs. From 

 this condition, the crust gradually rose again to the pres- 

 ent condition of things. 



Similar changes seem to have occurred everywhere in 

 high-latitude regions, but we are not sure that they were 

 absolutely contemporaneous. Therefore it will be best to 

 take the whole series of changes right through for each 

 locality. We commence with the Eastern United States, 

 because it has been best studied there. 



QUATERNARY IN" EASTERN" NORTH AMERICA. 



1. Glacial Epoch. 



The Drift. The phenomena now about to be de- 

 scribed are extremely varied ; but, as they exist all over 

 the Northern United States, we insist that every one 

 observe for himself. What we say is meant only as a 



All over the northern portion of our country, from 38 

 to 40 latitude northward, mantling over hill and dale, 

 over mountain and valley, is found a peculiar deposit or 

 soil composed of a heterogeneous mixture of earth, gravel, 

 pebbles, and rock-fragments of all sizes. As this material 

 has evidently been shifted and sometimes brought from a 

 long distance, it is called Drift. It is impossible to make 

 a description which will apply to all cases, but almost 

 everywhere the lower part in contact with the bed-rock 

 consists of stiff clay with disseminated stones rounded or 

 partly rounded, and scratched (Fig. 346). This is called 

 the stony-clay or ho wider -clay. It is exactly like the 

 ground moraine of a glacier, mentioned on page 58. In 

 places are found heaps or dumps of loose materials sim- 

 ilar to the top moraine of glaciers. In places the ma- 



