652 THE PLEISTOCENE PERIOD 



and deposition were in progress, and non-glacial Pleistocene forma- 

 tions are widespread. Under the varied conditions of the period, 

 various classes of deposits were made, among which were the fol- 

 lowing: (i) Eolian deposits, conspicuous along many shores and 

 rivers, and in sundry arid regions, and inconspicuous as dust over 

 much larger areas. (2) Flumatile deposits, made by streams (a) 

 with, and (b) without, connection with the ice. These deposits occur 

 along most streams of low gradient, and along many others. Kin- 

 dred deposits were made by sheet-floods and temporary streams, 

 even far from the courses of permanent streams. (3) Lacustrine 

 deposits of both the glacial and non-glacial types, made in existing 

 lakes and about their borders, and also over the sites of the numerous 

 lakes which have become extinct since the beginning of the period. 

 (4) Deposits made by springs. (5) Terrestrial organic deposits 

 (peat, calcareous marl, etc.) occur outside the area directly affected 

 by the ice, but are more common in the ponds and marshes to which 

 glaciation gave rise. (6) Marine deposits, on lands submerged 

 during the Pleistocene period, and doubtless over essentially all of 

 the ocean bottom. (7) Volcanic rocks of Pleistocene age are found 

 in our continent, chiefly west of the Rocky Mountains, though 

 volcanic dust is distributed widely on the Great Plains. All these 

 kinds of deposits were doubtless made at other periods, but have 

 not been preserved so generally. 



The average thickness of the Pleistocene deposits is not great. 



Pleistocene accumulations of debris at the bases of mountains are 



several hundreds of feet thick in some places; but otherwise the 



thickness of non-glacial Pleistocene deposits rarely exceeds a few 



^score feet. 



Atlantic and Gulf coasts : Columbia series. On the Coastal Plain 

 of the Atlantic and the Gulf of Mexico, there is a widespread but 

 thin body of gravel, sand, loam, and clay, referred to the Pleistocene 

 period. It ranges from sea-level up to altitudes of several hundred 

 feet, though most of it lies below 200 feet. All of the non-glacial 

 post-Tertiary deposits of the Atlantic and Gulf plains were formerly 

 grouped together under the name Columbia; but the materials 

 formerly grouped under this name represent at least three some- 

 what distinct stages of deposition. 1 



The oldest subdivision of the Columbia series (Qc, Fig. 535) is 



1 Reports of the State Geologist of New Jersey, 1897-1900; also Philadelphia 

 folio U. S. Geol. Surv. 



