THE QUATERNARY PERIOD 365 



of greatest submergence, and that the subsidence was most toward 

 the north. That this greatest submergence occurred after the 

 close of the Ice age in this region, is proved by the fact that the 

 now raised beaches and marine deposits rest upon the last or Wis- 

 consin ice drift. 



The most recent movement of the earth's crust in the region 

 under discussion was the very gradual elevation which expelled 

 the Champlain Sea and left the land at its present altitude. The 

 altitudes of the raised Champlain beaches show that the greatest 

 elevation was on the north. The warping of the Iroquois Lake 

 beaches already described occurred at this same time. Actual 

 surveys during the past century have proved that this upward 

 movement in the northern Great Lakes region is still progressing 

 at the rate of 5 inches in 100 miles in 100 years. 



QUATEKNARY CONDITIONS IN THE NON-GLACIATED REGIONS 



Over many parts of the continent there was deposition of sed- 

 iments during Quaternary time outside of the glaciated area, but 

 little or nothing can be done by way of correlating these with 

 different glacial and interglacial stages because of the lack of the 

 usual means of comparison. These deposits were of various sorts, 

 including those of river flood-plain, wind, terrestrial, lacustrine, 

 volcanic, and marine origin. 



Atlantic and Gulf Coasts. — On the Atlantic and Gulf Coastal 

 Plains, and in addition to the Lafayette (Pliocene?) already de- 

 scribed, there is a well-known series of unconsolidated deposits of 

 sands, gravels, clays, etc., usually comprised under the name 

 Columbia. Like the Lafayette, the Columbia is wholly a surficial 

 deposit but at lower altitudes, never rising more than a few hun- 

 dred feet above sea level and generally less than 200 feet. On the 

 north Atlantic Coastal . Plain, at least, the Columbia is pretty 

 clearly divisible into three formations (Sunderland, Wicomico, 

 and Talbot), each of which is represented topographically by a 

 more or less distinct terrace with the oldest at the top. 



There has been much difference of opinion regarding the origin 

 and significance of these Columbia deposits, but they are now quite 

 certainly known to be marine terraces. According to Shattuck, 1 

 each of the formations and terraces of the Columbia is explained 



1 G. B. Shattuck: Pliocene and Pleistocene, Md. Geol. Survey, p. 137. 



